:root{--primary-color: #4A90E2;--primary-dark: #357ABD;--primary-light: #6BA8E9;--secondary-color: #FF6B6B;--accent-color: #4ECDC4;--success-color: #28A745;--warning-color: #FFC107;--error-color: #DC3545;--background-color: #F8F9FA;--card-background: #FFFFFF;--text-primary: #2C3E50;--text-secondary: #6C757D;--text-muted: #95A5A6;--border-color: #E9ECEF;--shadow-color: rgba(0, 0, 0, .1);--gradient-primary: linear-gradient(135deg, var(--primary-color), var(--primary-dark));--gradient-secondary: linear-gradient(135deg, var(--secondary-color), #FF5252);--gradient-accent: linear-gradient(135deg, var(--accent-color), #26A69A);--font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", sans-serif;--font-size-xs: .75rem;--font-size-sm: .875rem;--font-size-base: 1rem;--font-size-lg: 1.125rem;--font-size-xl: 1.25rem;--font-size-2xl: 1.5rem;--font-size-3xl: 1.875rem;--font-size-4xl: 2.25rem;--spacing-xs: .25rem;--spacing-sm: .5rem;--spacing-md: 1rem;--spacing-lg: 1.5rem;--spacing-xl: 2rem;--spacing-2xl: 3rem;--border-radius-sm: .375rem;--border-radius-md: .5rem;--border-radius-lg: .75rem;--border-radius-xl: 1rem;--shadow-sm: 0 1px 3px var(--shadow-color);--shadow-md: 0 4px 6px var(--shadow-color);--shadow-lg: 0 10px 15px var(--shadow-color);--shadow-xl: 0 20px 25px var(--shadow-color)}*{margin:0;padding:0;box-sizing:border-box}html{scroll-behavior:smooth}body{font-family:var(--font-family);font-size:var(--font-size-base);line-height:1.6;color:var(--text-primary);background-color:var(--background-color);-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}h1,h2,h3,h4,h5,h6{font-weight:600;line-height:1.2;margin-bottom:var(--spacing-md)}h1{font-size:var(--font-size-4xl)}h2{font-size:var(--font-size-3xl)}h3{font-size:var(--font-size-2xl)}h4{font-size:var(--font-size-xl)}h5{font-size:var(--font-size-lg)}h6{font-size:var(--font-size-base)}p{margin-bottom:var(--spacing-md);color:var(--text-secondary)}.container{max-width:1200px;margin:0 auto;padding:0 var(--spacing-lg)}.section{padding:var(--spacing-2xl) 0}.btn{display:inline-flex;align-items:center;justify-content:center;gap:var(--spacing-sm);padding:var(--spacing-md) var(--spacing-lg);border:none;border-radius:var(--border-radius-md);font-size:var(--font-size-base);font-weight:500;text-decoration:none;cursor:pointer;transition:all .3s ease;position:relative;overflow:hidden}.btn:disabled{opacity:.6;cursor:not-allowed;transform:none!important}.btn-primary{background:var(--gradient-primary);color:#fff}.btn-primary:hover:not(:disabled){transform:translateY(-2px);box-shadow:var(--shadow-lg)}.btn-secondary{background:var(--gradient-secondary);color:#fff}.btn-secondary:hover:not(:disabled){transform:translateY(-2px);box-shadow:var(--shadow-lg)}.btn-outline{background:transparent;border:2px solid var(--primary-color);color:var(--primary-color)}.btn-outline:hover:not(:disabled){background:var(--primary-color);color:#fff;transform:translateY(-2px)}.btn-ghost{background:transparent;color:var(--text-secondary);border:1px solid transparent}.btn-ghost:hover:not(:disabled){background:var(--background-color);border-color:var(--border-color)}.form-group{margin-bottom:var(--spacing-lg)}.form-label{display:block;margin-bottom:var(--spacing-sm);font-weight:500;color:var(--text-primary)}.form-control{width:100%;padding:var(--spacing-md);border:1px solid var(--border-color);border-radius:var(--border-radius-md);font-size:var(--font-size-base);transition:all .3s ease;background-color:var(--card-background)}.form-control:focus{outline:none;border-color:var(--primary-color);box-shadow:0 0 0 3px #4a90e21a}.form-control:disabled{background-color:var(--background-color);color:var(--text-muted)}.form-select{-webkit-appearance:none;-moz-appearance:none;appearance:none;background-image:url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 20 20'%3e%3cpath stroke='%236b7280' stroke-linecap='round' stroke-linejoin='round' stroke-width='1.5' d='m6 8 4 4 4-4'/%3e%3c/svg%3e");background-position:right .5rem center;background-repeat:no-repeat;background-size:1.5em 1.5em;padding-right:2.5rem}.card{background:var(--card-background);border-radius:var(--border-radius-lg);box-shadow:var(--shadow-md);border:1px solid var(--border-color);overflow:hidden;transition:all .3s ease}.card:hover{box-shadow:var(--shadow-lg);transform:translateY(-2px)}.card-header{padding:var(--spacing-lg);border-bottom:1px solid var(--border-color);background:var(--gradient-primary);color:#fff}.card-body{padding:var(--spacing-lg)}.card-footer{padding:var(--spacing-lg);border-top:1px solid var(--border-color);background-color:var(--background-color)}.nav-tabs{display:flex;border-bottom:1px solid var(--border-color);margin-bottom:var(--spacing-lg)}.nav-tab{padding:var(--spacing-md) var(--spacing-lg);background:none;border:none;color:var(--text-secondary);cursor:pointer;border-bottom:2px solid transparent;transition:all .3s ease;font-weight:500}.nav-tab.active{color:var(--primary-color);border-bottom-color:var(--primary-color)}.nav-tab:hover:not(.active){color:var(--text-primary);background-color:var(--background-color)}.chat-container{display:flex;flex-direction:column;height:600px;background:var(--card-background);border-radius:var(--border-radius-lg);box-shadow:var(--shadow-md);overflow:hidden}.chat-header{padding:var(--spacing-lg);background:var(--gradient-primary);color:#fff;display:flex;justify-content:space-between;align-items:center}.chat-messages{flex:1;overflow-y:auto;padding:var(--spacing-lg);display:flex;flex-direction:column;gap:var(--spacing-md)}.message{max-width:70%;padding:var(--spacing-md);border-radius:var(--border-radius-lg);position:relative;animation:slideIn .3s ease}@keyframes slideIn{0%{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}.message.user{align-self:flex-end;background:var(--gradient-primary);color:#fff;border-bottom-right-radius:var(--border-radius-sm)}.message.assistant{align-self:flex-start;background:var(--background-color);color:var(--text-primary);border:1px solid var(--border-color);border-bottom-left-radius:var(--border-radius-sm)}.message-content{line-height:1.5}.message-time{font-size:var(--font-size-xs);opacity:.7;margin-top:var(--spacing-xs)}.chat-input-area{padding:var(--spacing-lg);border-top:1px solid var(--border-color);background:var(--card-background)}.chat-input-form{display:flex;gap:var(--spacing-md);align-items:flex-end}.chat-input{flex:1;resize:none;min-height:60px;max-height:120px}.file-upload-area{display:flex;align-items:flex-end;gap:var(--spacing-md);margin-bottom:var(--spacing-md)}.file-input{display:none}.file-upload-btn{display:inline-flex;align-items:center;gap:var(--spacing-sm);padding:var(--spacing-sm) var(--spacing-md);background:var(--background-color);border:1px solid var(--border-color);border-radius:var(--border-radius-md);cursor:pointer;transition:all .3s ease}.file-selected{display:flex;align-items:center;gap:var(--spacing-sm);padding:var(--spacing-sm) var(--spacing-md);background:var(--success-color);color:#fff;border-radius:var(--border-radius-md);font-size:var(--font-size-sm)}.exam-generator{background:var(--card-background);border-radius:var(--border-radius-lg);padding:var(--spacing-xl);box-shadow:var(--shadow-md)}.exam-form{display:grid;gap:var(--spacing-lg);margin-bottom:var(--spacing-lg)}.exam-preview{background:var(--background-color);border-radius:var(--border-radius-md);padding:var(--spacing-lg);margin-top:var(--spacing-lg)}.upload-area{border:2px dashed var(--border-color);border-radius:var(--border-radius-lg);padding:var(--spacing-2xl);text-align:center;cursor:pointer;transition:all .3s ease;background:var(--card-background)}.upload-area:hover{border-color:var(--primary-color);background:#4a90e20d}.upload-area.dragover{border-color:var(--primary-color);background:#4a90e21a}.upload-icon{font-size:3rem;color:var(--text-muted);margin-bottom:var(--spacing-md)}.status{padding:var(--spacing-md);border-radius:var(--border-radius-md);margin:var(--spacing-md) 0;font-weight:500}.status.success{background:#28a7451a;color:var(--success-color);border-left:4px solid var(--success-color)}.status.error{background:#dc35451a;color:var(--error-color);border-left:4px solid var(--error-color)}.status.warning{background:#ffc1071a;color:var(--warning-color);border-left:4px solid var(--warning-color)}.status.info{background:#4a90e21a;color:var(--primary-color);border-left:4px solid var(--primary-color)}.loading{display:inline-block;width:20px;height:20px;border:3px solid #f3f3f3;border-top:3px solid var(--primary-color);border-radius:50%;animation:spin 1s linear infinite}@keyframes spin{0%{transform:rotate(0)}to{transform:rotate(360deg)}}.loading-overlay{position:absolute;top:0;left:0;right:0;bottom:0;background:#fffc;display:flex;align-items:center;justify-content:center;z-index:10}.user-profile{display:flex;align-items:center;gap:var(--spacing-md)}.user-info{display:flex;flex-direction:column}.user-name{font-weight:600;font-size:var(--font-size-sm)}.user-email{font-size:var(--font-size-xs);color:var(--text-muted)}.modal-overlay{position:fixed;top:0;left:0;right:0;bottom:0;background:#00000080;display:flex;align-items:center;justify-content:center;z-index:1000;padding:var(--spacing-lg)}.modal-content{background:var(--card-background);border-radius:var(--border-radius-lg);width:100%;max-width:500px;max-height:90vh;overflow-y:auto;box-shadow:var(--shadow-xl);animation:modalSlideIn .3s ease}@keyframes modalSlideIn{0%{opacity:0;transform:translateY(-20px) scale(.95)}to{opacity:1;transform:translateY(0) scale(1)}}.modal-header{padding:var(--spacing-lg);border-bottom:1px solid var(--border-color);display:flex;justify-content:space-between;align-items:center}.modal-title{font-size:var(--font-size-xl);font-weight:600;color:var(--text-primary)}.modal-close{background:none;border:none;font-size:var(--font-size-xl);cursor:pointer;color:var(--text-muted);padding:var(--spacing-xs);border-radius:var(--border-radius-sm)}.modal-close:hover{background:var(--background-color);color:var(--text-primary)}.modal-body{padding:var(--spacing-lg)}.modal-footer{padding:var(--spacing-lg);border-top:1px solid var(--border-color);display:flex;gap:var(--spacing-md);justify-content:flex-end}@media (max-width: 768px){.container{padding:0 var(--spacing-md)}.section{padding:var(--spacing-xl) 0}.chat-container{height:500px}.message{max-width:85%}.chat-input-form{flex-direction:column;gap:var(--spacing-md)}.exam-form{grid-template-columns:1fr}.nav-tabs{flex-wrap:wrap}.nav-tab{flex:1;min-width:120px;text-align:center}.modal-content{margin:var(--spacing-md);width:calc(100% - var(--spacing-xl))}h1{font-size:var(--font-size-3xl)}h2{font-size:var(--font-size-2xl)}h3{font-size:var(--font-size-xl)}}:root{--sidebar-width: 260px;--sidebar-collapsed-width: 56px;--header-height: 72px;--input-height: 100px}.chatgpt-sidebar{width:var(--sidebar-width);background:#202123;color:#fff;display:flex;flex-direction:column;height:100vh;position:fixed;left:0;top:0;z-index:1000;border-right:1px solid #343541;transition:width .2s ease}.chatgpt-sidebar.collapsed{width:0;overflow:hidden}.chatgpt-sidebar .nav-text{transition:opacity .15s ease,width .15s ease}.chatgpt-sidebar.collapsed .sidebar-nav,.chatgpt-sidebar.collapsed .conversation-section,.chatgpt-sidebar.collapsed .sidebar-bottom,.chatgpt-sidebar.collapsed .section-header,.chatgpt-sidebar.collapsed .conversation-list,.chatgpt-sidebar.collapsed .no-conversations,.chatgpt-sidebar.collapsed .sidebar-user,.chatgpt-sidebar.collapsed .sidebar-logout,.chatgpt-sidebar.collapsed .nav-text,.chatgpt-sidebar.collapsed .nav-icon{display:none!important}.sidebar-toggle-btn{position:absolute;left:25px;top:12px;width:36px;height:36px;border-radius:50%;border:none;background:#111;color:#fff;box-shadow:0 2px 8px #00000059;cursor:pointer;z-index:1100;transition:all .2s ease}.chatgpt-sidebar.collapsed .sidebar-toggle-btn{right:auto;left:50%;transform:translate(-50%)}.main-workspace{margin-left:var(--sidebar-width);background:#fff;min-height:100vh;display:flex;flex-direction:column;transition:margin-left .2s ease}.workspace-header{position:fixed;top:0;left:var(--sidebar-width);right:0;height:var(--header-height);display:flex;align-items:center;justify-content:space-between;padding:0 1rem;z-index:900;background:#f7f7f8;border-bottom:1px solid #d1d5db}.chat-container{margin-top:var(--header-height);margin-bottom:var(--input-height);padding:1rem 1.5rem;height:calc(100vh - var(--header-height) - var(--input-height));display:flex;flex-direction:column;overflow:hidden}.exam-generator,.upload-interface{margin-top:var(--header-height);padding:1rem 1.5rem;min-height:calc(100vh - var(--header-height));overflow-y:auto}.chat-messages{flex:1 1 auto;overflow-y:auto;padding-right:.5rem}.chat-input-container{position:fixed;bottom:0;left:var(--sidebar-width);right:0;height:var(--input-height);padding:12px 16px;background:var(--card-background);border-top:1px solid var(--border-color);z-index:950;display:flex;align-items:flex-end;gap:1rem}.chat-input-container .file-upload-area{margin-bottom:0}.chat-input-form{width:100%;display:flex;gap:.75rem;align-items:center}.chat-input{min-height:48px;max-height:120px}@media (max-width: 768px){body{overflow:hidden}.app-container{display:flex;flex-direction:column;height:100vh}.chatgpt-sidebar{position:relative;width:100%;height:auto;max-height:50vh;overflow-y:auto;background:#202123;transition:max-height .3s ease,transform .3s ease;transform:translateY(0);z-index:100}.chatgpt-sidebar.collapsed{max-height:0;transform:translateY(-100%);overflow:hidden}.sidebar-toggle-btn{position:fixed;left:16px;top:16px;width:40px;height:40px;border-radius:8px;background:#2d2d2d;border:1px solid #4a4a4a;color:#fff;z-index:1000;cursor:pointer;display:flex;align-items:center;justify-content:center;font-size:18px;box-shadow:0 2px 8px #0003;transition:all .2s ease}.sidebar-toggle-btn:hover{background:#3a3a3a;transform:scale(1.05)}.main-workspace{flex:1;margin-left:0;width:100%;display:flex;flex-direction:column;overflow:hidden}.main-workspace.sidebar-collapsed{margin-left:0}.workspace-header{position:relative;left:0;right:0;padding:16px 60px 16px 16px;height:auto;background:#f8f9fa;border-bottom:1px solid #e0e0e0;flex-shrink:0}.main-workspace.sidebar-collapsed .workspace-header{left:0}.grade-subject-selector{position:relative;flex-direction:column;gap:8px;width:100%;padding:8px 0}.grade-subject-form{display:flex;flex-direction:column;gap:8px;width:100%}.grade-subject-form select{min-width:auto;width:100%;font-size:14px;padding:10px 12px;border-radius:8px;border:1px solid #ddd}.language-toggle{flex-wrap:wrap;gap:8px;justify-content:flex-start;width:100%;margin-top:8px}.lang-btn{flex:1;min-width:100px;padding:10px 14px;font-size:14px;border-radius:20px}.chat-container{flex:1;margin:0;padding:12px;overflow:hidden;display:flex;flex-direction:column}.chat-messages{flex:1;overflow-y:auto;padding:0;gap:16px;margin-bottom:12px}.message{max-width:85%;padding:12px 16px;border-radius:16px;font-size:15px;line-height:1.4}.message.user{border-bottom-right-radius:4px}.message.assistant{border-bottom-left-radius:4px}.chat-input-container{position:relative;bottom:auto;left:auto;right:auto;padding:12px 16px 16px;background:#fff;border-top:1px solid #e0e0e0;flex-shrink:0}.file-upload-area{margin-bottom:8px;display:flex;flex-wrap:wrap;gap:8px;align-items:center}.file-upload-btn{padding:8px 12px;font-size:14px;border-radius:20px;background:#f0f0f0;border:1px solid #ddd}.file-selected{padding:6px 12px;background:#e8f5e8;border-radius:16px;font-size:13px;display:flex;align-items:center;gap:8px}.chat-input-form{display:flex;gap:8px;align-items:flex-end}.chat-input{flex:1;min-height:44px;max-height:120px;padding:12px 16px;border:1px solid #ddd;border-radius:22px;resize:none;font-size:16px;line-height:1.4;background:#f8f9fa}.chat-input:focus{border-color:#4a90e2;background:#fff;outline:none}.send-btn{width:44px;height:44px;border-radius:50%;border:none;background:#4a90e2;color:#fff;display:flex;align-items:center;justify-content:center;font-size:18px;cursor:pointer;transition:all .2s ease;flex-shrink:0}.send-btn:hover:not(:disabled){background:#357abd;transform:scale(1.05)}.send-btn:disabled{background:#ccc;transform:none}.chat-input-form{gap:6px!important}.chat-input{flex:1!important;min-width:0!important}.send-btn{width:40px!important;height:40px!important;min-width:40px!important;font-size:16px!important;flex-shrink:0!important}.file-upload-btn{padding:8px 10px!important;font-size:14px!important;min-width:auto!important;white-space:nowrap!important}.welcome-message{text-align:center;padding:40px 20px}.welcome-message h3{font-size:24px;margin-bottom:16px}.welcome-message p{font-size:16px;margin-bottom:24px;color:#666}.welcome-tips{display:flex;flex-direction:column;gap:12px;text-align:left}.tip{padding:12px 16px;background:#f0f8ff;border-radius:12px;font-size:14px;border-left:3px solid #4A90E2}}@media (max-width: 480px){.sidebar-toggle-btn{left:12px;top:12px;width:36px;height:36px}.workspace-header{padding:12px 48px 12px 12px;height:70px}.chat-container{margin-top:70px;margin-bottom:110px;height:calc(100vh - 180px)}.grade-subject-form select{padding:10px 12px;font-size:14px}.lang-btn{padding:6px 10px;font-size:13px}}.text-center{text-align:center}.text-left{text-align:left}.text-right{text-align:right}.mt-0{margin-top:0}.mt-1{margin-top:var(--spacing-xs)}.mt-2{margin-top:var(--spacing-sm)}.mt-3{margin-top:var(--spacing-md)}.mt-4{margin-top:var(--spacing-lg)}.mt-5{margin-top:var(--spacing-xl)}.mb-0{margin-bottom:0}.mb-1{margin-bottom:var(--spacing-xs)}.mb-2{margin-bottom:var(--spacing-sm)}.mb-3{margin-bottom:var(--spacing-md)}.mb-4{margin-bottom:var(--spacing-lg)}.mb-5{margin-bottom:var(--spacing-xl)}.p-0{padding:0}.p-1{padding:var(--spacing-xs)}.p-2{padding:var(--spacing-sm)}.p-3{padding:var(--spacing-md)}.p-4{padding:var(--spacing-lg)}.p-5{padding:var(--spacing-xl)}.d-flex{display:flex}.d-grid{display:grid}.d-none{display:none}.d-block{display:block}.d-inline{display:inline}.d-inline-block{display:inline-block}.justify-center{justify-content:center}.justify-between{justify-content:space-between}.justify-end{justify-content:flex-end}.align-center{align-items:center}.align-start{align-items:flex-start}.align-end{align-items:flex-end}.flex-column{flex-direction:column}.flex-row{flex-direction:row}.flex-wrap{flex-wrap:wrap}.gap-1{gap:var(--spacing-xs)}.gap-2{gap:var(--spacing-sm)}.gap-3{gap:var(--spacing-md)}.gap-4{gap:var(--spacing-lg)}.gap-5{gap:var(--spacing-xl)}.w-100{width:100%}.h-100{height:100%}.landing-page{min-height:100vh}.hero-section{position:relative;min-height:100vh;display:flex;align-items:center;background:linear-gradient(135deg,var(--primary-color) 0%,var(--primary-dark) 100%);color:#fff;overflow:hidden}.hero-background{position:absolute;top:0;left:0;right:0;bottom:0;background:url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" fill="rgba(255,255,255,0.05)"><circle cx="20" cy="20" r="2"/><circle cx="80" cy="40" r="1.5"/><circle cx="40" cy="80" r="1"/><circle cx="60" cy="20" r="1.2"/><circle cx="90" cy="70" r="0.8"/></svg>')}.hero-content{position:relative;z-index:2;max-width:800px;margin:0 auto}.hero-badge{display:inline-block;background:#fff3;padding:.5rem 1rem;border-radius:2rem;font-size:var(--font-size-sm);margin-bottom:1rem;-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px)}.hero-title{font-size:4rem;font-weight:700;margin-bottom:1rem;background:linear-gradient(45deg,#fff,#f0f8ff);-webkit-background-clip:text;-webkit-text-fill-color:transparent;background-clip:text}.hero-subtitle{font-size:1.5rem;color:#333;margin-bottom:1rem;font-weight:600}.hero-description{font-size:1.1rem;line-height:1.6;margin-bottom:2.5rem;color:#ffffffe6;max-width:600px;margin-left:auto;margin-right:auto;font-weight:400}.btn-hero{padding:1rem 2rem;font-size:1.1rem;border-radius:2rem;background:#ffffffe6;color:var(--primary-color);border:2px solid rgba(255,255,255,.8);transition:all .3s ease;font-weight:600}.btn-hero:hover{background:#fff;color:var(--primary-dark);transform:translateY(-2px);box-shadow:0 10px 30px #0000004d}.hero-stats{display:flex;justify-content:center;gap:3rem;margin-top:3rem}.stat-item{text-align:center}.stat-number{font-size:2rem;font-weight:700;margin-bottom:.5rem}.stat-label{font-size:.9rem;opacity:.8}.features-section{padding:6rem 0;background:var(--background-color)}.section-header{margin-bottom:4rem}.section-header h2{font-size:3rem;color:var(--text-primary);margin-bottom:1rem}.section-subtitle{font-size:1.2rem;color:var(--text-secondary);max-width:600px;margin:0 auto}.features-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(350px,1fr));gap:2rem}.feature-card{background:var(--card-background);padding:2.5rem;border-radius:1rem;box-shadow:var(--shadow-lg);transition:all .3s ease;text-align:center}.feature-card:hover{transform:translateY(-5px);box-shadow:var(--shadow-xl)}.feature-icon{font-size:3rem;margin-bottom:1.5rem}.feature-card h3{font-size:1.5rem;margin-bottom:1rem;color:var(--text-primary)}.feature-card p{color:var(--text-secondary);line-height:1.6}.how-it-works-section{padding:6rem 0;background:#fff}.timeline{display:grid;grid-template-columns:repeat(auto-fit,minmax(250px,1fr));gap:2rem;max-width:1000px;margin:0 auto}.timeline-step{text-align:center;position:relative}.step-number{width:60px;height:60px;background:var(--gradient-primary);color:#fff;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1.5rem;font-weight:700;margin:0 auto 1.5rem;position:relative;z-index:2}.step-content h3{font-size:1.3rem;margin-bottom:1rem;color:var(--text-primary)}.step-content p{color:var(--text-secondary);line-height:1.6}.testimonials-section{padding:6rem 0;background:var(--background-color)}.testimonials-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(300px,1fr));gap:2rem;max-width:1000px;margin:0 auto}.testimonial-card{background:var(--card-background);padding:2rem;border-radius:1rem;box-shadow:var(--shadow-md)}.testimonial-content{font-style:italic;margin-bottom:1.5rem;line-height:1.6;color:var(--text-primary)}.testimonial-author{border-top:1px solid var(--border-color);padding-top:1rem}.author-name{font-weight:600;color:var(--text-primary)}.author-role{font-size:.9rem;color:var(--text-secondary)}.cta-section{padding:6rem 0;background:linear-gradient(135deg,var(--primary-color) 0%,var(--primary-dark) 100%);color:#fff;text-align:center}.cta-section h2{font-size:3rem;margin-bottom:1rem}.cta-description{font-size:1.2rem;max-width:600px;margin:0 auto 2rem;opacity:.9}.btn-cta{padding:1.2rem 3rem;font-size:1.2rem;border-radius:2rem;background:#fff3;border:1px solid rgba(255,255,255,.3);-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px);margin-bottom:2rem}.cta-features{display:flex;justify-content:center;gap:1rem;flex-wrap:wrap}.feature-tag{background:#ffffff1a;padding:.5rem 1rem;border-radius:1rem;font-size:.9rem}.landing-footer{background:var(--text-primary);color:#fff;padding:3rem 0 1rem}.footer-content{display:grid;grid-template-columns:2fr 3fr;gap:3rem;margin-bottom:2rem}.footer-brand h3{font-size:1.8rem;margin-bottom:1rem}.footer-links{display:grid;grid-template-columns:repeat(3,1fr);gap:2rem}.footer-section h4{margin-bottom:1rem;font-size:1.1rem}.footer-section a{display:block;color:#ffffffb3;text-decoration:none;margin-bottom:.5rem;transition:color .3s ease}.footer-section a:hover{color:#fff}.footer-bottom{border-top:1px solid rgba(255,255,255,.1);padding-top:2rem;text-align:center;color:#fff9}@media (max-width: 768px){.hero-title{font-size:2.5rem}.hero-subtitle{font-size:1.2rem}.hero-stats{flex-direction:column;gap:1.5rem}.features-grid,.timeline,.footer-content,.footer-links{grid-template-columns:1fr}.cta-features{flex-direction:column;align-items:center}}.main-app{min-height:100vh;background:var(--background-color)}.top-bar{background:var(--card-background);border-bottom:1px solid var(--border-color);padding:1rem 0;box-shadow:var(--shadow-sm)}.top-bar-content{display:flex;justify-content:space-between;align-items:center;gap:2rem}.grade-subject-pill{background:var(--gradient-primary);color:#fff;padding:.5rem 1rem;border-radius:2rem;font-weight:500;display:flex;align-items:center;gap:.5rem}.edit-btn{background:#fff3;border:none;color:#fff;border-radius:50%;width:24px;height:24px;display:flex;align-items:center;justify-content:center;cursor:pointer;font-size:.8rem}.grade-subject-form select{min-width:150px}.language-toggle{display:flex;background:var(--background-color);border-radius:var(--border-radius-md);padding:.25rem;border:1px solid var(--border-color)}.lang-btn{padding:.5rem 1rem;border:none;background:transparent;color:var(--text-secondary);border-radius:var(--border-radius-sm);cursor:pointer;transition:all .3s ease;font-size:.9rem}.app-layout{display:grid;grid-template-columns:300px 1fr;min-height:calc(100vh - 80px)}.conversation-sidebar{background:var(--card-background);border-right:1px solid var(--border-color);display:flex;flex-direction:column}.sidebar-header{padding:1.5rem;border-bottom:1px solid var(--border-color);display:flex;justify-content:space-between;align-items:center}.sidebar-header h3{margin:0;font-size:1.1rem;color:var(--text-primary)}.new-chat-btn{background:var(--primary-color);color:#fff;border:none;border-radius:var(--border-radius-md);padding:.5rem 1rem;font-size:.9rem;cursor:pointer;transition:all .3s ease}.new-chat-btn:hover{background:var(--primary-dark)}.conversation-item{padding:1rem;border-radius:var(--border-radius-md);cursor:pointer;transition:all .3s ease;margin-bottom:.5rem}.conversation-item:hover{background:var(--background-color)}.conversation-title{font-weight:500;color:var(--text-primary);margin-bottom:.25rem}.conversation-meta{font-size:.8rem;color:var(--text-muted)}.no-conversations{text-align:center;color:var(--text-muted);padding:2rem;font-style:italic}.main-content{display:flex;flex-direction:column;padding:0}.feature-tabs{display:flex;background:var(--card-background);border-bottom:1px solid var(--border-color);padding:0 2rem}.feature-tab{padding:1rem 2rem;border:none;background:transparent;color:var(--text-secondary);border-bottom:3px solid transparent;cursor:pointer;transition:all .3s ease;font-weight:500;font-size:1rem;display:flex;align-items:center;gap:.5rem}.feature-tab.active{color:var(--primary-color);border-bottom-color:var(--primary-color);background:#4a90e20d}.feature-tab:hover:not(.active){color:var(--text-primary);background:var(--background-color)}.user-profile-section{display:flex;justify-content:space-between;align-items:center;padding:1rem 2rem;background:var(--card-background);border-bottom:1px solid var(--border-color)}.user-info{display:flex;align-items:center;gap:1rem}.user-avatar{width:40px;height:40px;border-radius:50%;object-fit:cover;border:2px solid var(--border-color)}.user-details{display:flex;flex-direction:column}.user-name{font-weight:600;font-size:.9rem;color:var(--text-primary)}.user-email{font-size:.8rem;color:var(--text-muted)}.logout-btn{background:var(--error-color);color:#fff;border:none;border-radius:var(--border-radius-md);padding:.5rem 1rem;font-weight:500;cursor:pointer;transition:all .3s ease}.logout-btn:hover{background:#c82333}.chat-interface{flex:1;display:flex;flex-direction:column;padding:0}.chat-container{flex:1;display:flex;flex-direction:column;background:var(--card-background);margin:0;border-radius:0;box-shadow:none}.chat-messages{flex:1;overflow-y:auto;padding:2rem;display:flex;flex-direction:column;gap:1.5rem}.welcome-message{text-align:center;padding:3rem 2rem;color:var(--text-secondary);max-width:600px;margin:0 auto}.tip{padding:.75rem;background:var(--background-color);border-radius:var(--border-radius-md);font-size:.9rem;border-left:3px solid var(--primary-color)}.message-avatar{width:40px;height:40px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1.2rem;flex-shrink:0}.message.user .message-avatar{background:var(--gradient-primary);order:2}.message.assistant .message-avatar{background:var(--gradient-secondary);order:1}.message-sender{font-weight:600;color:var(--text-primary);font-size:.9rem}.message-time{font-size:.8rem;color:var(--text-muted)}.message-file{background:var(--background-color);padding:.5rem .75rem;border-radius:var(--border-radius-sm);font-size:.9rem;border:1px solid var(--border-color)}.message-bubble{padding:1rem 1.25rem;border-radius:var(--border-radius-lg);line-height:1.5;word-wrap:break-word}.message.user .message-bubble{background:var(--gradient-primary);color:#fff;border-bottom-right-radius:var(--border-radius-sm)}.message.assistant .message-bubble{background:var(--background-color);color:var(--text-primary);border:1px solid var(--border-color);border-bottom-left-radius:var(--border-radius-sm)}.message-actions{margin-top:.5rem}.feedback-btn{background:transparent;border:1px solid var(--border-color);color:var(--text-secondary);padding:.25rem .75rem;border-radius:var(--border-radius-sm);font-size:.8rem;cursor:pointer;transition:all .3s ease}.feedback-btn:hover{background:var(--background-color);color:var(--text-primary)}.loading-message{display:flex;align-items:center;gap:.75rem;color:var(--text-muted);font-style:italic}.chat-input-container{border-top:1px solid var(--border-color);padding:1.5rem 2rem;background:var(--card-background)}.file-upload-area{display:flex;align-items:center;gap:1rem;margin-bottom:1rem;flex-wrap:wrap}.file-upload-btn{display:inline-flex;align-items:center;gap:.5rem;padding:.5rem 1rem;background:var(--background-color);border:1px solid var(--border-color);border-radius:var(--border-radius-md);cursor:pointer;transition:all .3s ease;font-size:.9rem}.file-selected{display:flex;align-items:center;gap:.75rem;padding:.5rem 1rem;background:var(--success-color);color:#fff;border-radius:var(--border-radius-md);font-size:.9rem}.remove-file-btn{background:transparent;border:none;color:#fff;cursor:pointer;padding:.25rem;border-radius:50%}.remove-file-btn:hover{background:#fff3}.chat-input-form{display:flex;gap:1rem;align-items:flex-end}.chat-input{flex:1;resize:none;min-height:60px;max-height:120px;padding:1rem;border:1px solid var(--border-color);border-radius:var(--border-radius-lg);font-size:1rem;line-height:1.5;transition:all .3s ease}.chat-input:focus{outline:none;border-color:var(--primary-color);box-shadow:0 0 0 3px #4a90e21a}.send-btn{background:var(--primary-color);color:#fff;border:none;border-radius:var(--border-radius-lg);width:50px;height:50px;display:flex;align-items:center;justify-content:center;cursor:pointer;transition:all .3s ease;font-size:1.2rem}.send-btn:disabled{background:var(--text-muted);cursor:not-allowed}.chatgpt-sidebar{width:260px;background:#202123;color:#fff;display:flex;flex-direction:column;height:100vh;position:fixed;left:0;top:0;z-index:1000;border-right:1px solid #343541}.nav-btn{width:100%;display:flex;align-items:center;gap:.75rem;padding:.75rem 1rem;background:transparent;border:1px solid #565869;border-radius:.5rem;color:#d1d5db;cursor:pointer;transition:all .2s ease;margin-bottom:.5rem;font-size:.9rem}.nav-btn:hover{background:#343541;border-color:#8e8ea0}.nav-btn.active{background:#343541;border-color:#10a37f;color:#10a37f}.nav-icon{font-size:1.1rem}.nav-text{font-weight:500}.conversation-section{flex:1;display:flex;flex-direction:column;overflow:hidden}.section-header{padding:1rem;border-bottom:1px solid #343541;display:flex;justify-content:space-between;align-items:center}.section-header h3{margin:0;font-size:.9rem;color:#d1d5db;font-weight:600}.new-chat-btn{background:#10a37f;color:#fff;border:none;border-radius:.375rem;padding:.5rem .75rem;font-size:.8rem;cursor:pointer;transition:all .2s ease}.new-chat-btn:hover{background:#0d8c6d}.conversation-list{flex:1;overflow-y:auto;padding:.5rem}.conversation-item{padding:.75rem;border-radius:.375rem;cursor:pointer;transition:all .2s ease;margin-bottom:.25rem}.conversation-item:hover{background:#343541}.conversation-title{font-size:.9rem;color:#d1d5db;margin-bottom:.25rem;font-weight:500}.conversation-meta{font-size:.75rem;color:#8e8ea0}.no-conversations{text-align:center;color:#8e8ea0;padding:2rem 1rem;font-style:italic;font-size:.9rem}.sidebar-bottom{padding:1rem;border-top:1px solid #343541;background:#202123}.sidebar-logo{display:flex;align-items:center;gap:.5rem;margin-bottom:1rem;font-weight:600;color:#d1d5db}.logo-icon{font-size:1.2rem}.sidebar-logout{width:100%;background:#ef4444;color:#fff;border:none;border-radius:.375rem;padding:.75rem;font-weight:500;cursor:pointer;transition:all .2s ease}.sidebar-logout:hover{background:#dc2626}.main-workspace{margin-left:260px;background:#fff;min-height:100vh;display:flex;flex-direction:column}.workspace-header{background:#f7f7f8;border-bottom:1px solid #d1d5db;padding:1rem 2rem;display:flex;justify-content:space-between;align-items:center}.grade-subject-selector{display:flex;align-items:center;gap:1rem}.grade-subject-display{display:flex;align-items:center}.grade-subject-pill{background:#10a37f;color:#fff;padding:.5rem 1rem;border-radius:2rem;font-weight:500;display:flex;align-items:center;gap:.5rem;font-size:.9rem}.edit-btn{background:#fff3;border:none;color:#fff;border-radius:50%;width:20px;height:20px;display:flex;align-items:center;justify-content:center;cursor:pointer;font-size:.7rem}.grade-subject-form{display:flex;gap:1rem;align-items:center}.grade-subject-form select{min-width:120px;font-size:.9rem}.language-toggle{display:flex;background:#fff;border-radius:.5rem;padding:.25rem;border:1px solid #d1d5db}.lang-btn{padding:.5rem .75rem;border:none;background:transparent;color:#6b7280;border-radius:.375rem;cursor:pointer;transition:all .2s ease;font-size:.9rem}.lang-btn.active{background:#10a37f;color:#fff}.chat-interface{flex:1;display:flex;flex-direction:column;background:#fff}.chat-container{flex:1;display:flex;flex-direction:column;max-width:800px;margin:0 auto;width:100%;padding:0 2rem}.chat-messages{flex:1;overflow-y:auto;padding:2rem 0;display:flex;flex-direction:column;gap:1.5rem}.welcome-message{text-align:center;padding:3rem 2rem;color:#6b7280;max-width:600px;margin:0 auto}.welcome-icon{font-size:4rem;margin-bottom:1rem}.welcome-tips{display:flex;flex-direction:column;gap:.75rem;margin-top:2rem}.tip{padding:.75rem;background:#f7f7f8;border-radius:.5rem;font-size:.9rem;border-left:3px solid #10a37f}.message{display:flex;gap:1rem;max-width:100%;animation:slideIn .3s ease}.message.user{justify-content:flex-end}.message.assistant{justify-content:flex-start}.message-avatar{width:30px;height:30px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1rem;flex-shrink:0}.message.user .message-avatar{background:#10a37f;order:2}.message.assistant .message-avatar{background:#8e8ea0;order:1}.message-content-wrapper{flex:1;max-width:70%;display:flex;flex-direction:column;gap:.5rem}.message.user .message-content-wrapper{align-items:flex-end}.message-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:.25rem}.message-sender{font-weight:600;color:#374151;font-size:.9rem}.message-time{font-size:.8rem;color:#9ca3af}.message-file{background:#f7f7f8;padding:.5rem .75rem;border-radius:.375rem;font-size:.9rem;border:1px solid #d1d5db}.message-bubble{padding:1rem 1.25rem;border-radius:1rem;line-height:1.5;word-wrap:break-word}.message.user .message-bubble{background:#10a37f;color:#fff;border-bottom-right-radius:.375rem}.message.assistant .message-bubble{background:#f7f7f8;color:#374151;border:1px solid #d1d5db;border-bottom-left-radius:.375rem}.chat-input-container{border-top:1px solid #d1d5db;padding:1.5rem 0;background:#fff;position:sticky;bottom:0}.exam-generator{flex:1;padding:2rem;max-width:600px;margin:var(--header-height) auto 0 auto;width:100%}.feature-card{background:#fff;border-radius:.75rem;box-shadow:0 1px 3px #0000001a;border:1px solid #d1d5db}.card-header{padding:1.5rem;border-bottom:1px solid #d1d5db;background:#f7f7f8}.card-header h3{margin:0;color:#374151;font-size:1.25rem}.card-body{padding:1.5rem}.upload-instructions{background:#f0f9ff;border:1px solid #bae6fd;border-radius:.5rem;padding:1rem;margin-bottom:1.5rem}.upload-instructions p{margin:0;color:#0369a1;font-size:.9rem;line-height:1.5}@media (max-width: 768px){.chatgpt-sidebar{width:100%;height:auto;position:relative;border-right:none;border-bottom:1px solid #343541}.main-workspace{margin-left:0}.workspace-header{flex-direction:column;gap:1rem;align-items:stretch}.grade-subject-selector{flex-direction:column;align-items:stretch}.grade-subject-form{flex-direction:column}.chat-container{padding:0 1rem}.chat-messages{padding:1rem 0}}.beta-warning-banner{background:#fffbeb;border:1px solid #fef3c7;border-radius:.5rem;margin:2rem auto;max-width:1200px;box-shadow:0 1px 3px #0000001a}.beta-content{display:flex;align-items:center;gap:1rem;padding:1rem 1.5rem;color:#92400e;font-size:.9rem;line-height:1.5}.beta-icon{font-size:1.2rem;flex-shrink:0}.beta-text{flex:1}.beta-badge{background:#f59e0b;color:#fff;font-size:.7rem;font-weight:600;padding:.2rem .5rem;border-radius:1rem;margin-left:.5rem;text-transform:uppercase;letter-spacing:.5px}.sidebar-user{display:flex;align-items:center;gap:.75rem;margin-bottom:1rem}.user-icon{font-size:1.2rem}.user-name{font-weight:500;color:#d1d5db;flex:1}.mission-modal{max-width:800px}.mission-body{padding:2rem}.mission-story{line-height:1.7;font-size:1.1rem}.mission-intro{font-size:1.2rem;color:#374151;margin-bottom:1.5rem;font-weight:500}.challenges-list{display:flex;flex-direction:column;gap:1rem;margin:1.5rem 0}.challenge-item{display:flex;align-items:center;gap:1rem;padding:1rem;background:#f0f9ff;border-radius:.5rem;border-left:4px solid #0ea5e9}.challenge-icon{font-size:1.5rem;flex-shrink:0}.mission-highlight{background:#fef3c7;padding:1rem;border-radius:.5rem;border-left:4px solid #f59e0b;margin:1.5rem 0;font-size:1.2rem;text-align:center}.mission-goals{margin:2rem 0}.mission-goals h3{color:#1e40af;margin-bottom:1.5rem;font-size:1.3rem}.goal-item{display:flex;align-items:flex-start;gap:1rem;margin-bottom:1.5rem;padding:1rem;background:#f8fafc;border-radius:.5rem}.goal-icon{font-size:1.5rem;flex-shrink:0;margin-top:.2rem}.vision-section{margin:2rem 0}.vision-section h3{color:#1e40af;margin-bottom:1rem;font-size:1.3rem}.vision-list{list-style:none;padding:0;margin:1rem 0}.vision-list li{display:flex;align-items:center;gap:.75rem;margin-bottom:.75rem;padding:.75rem;background:#f0f9ff;border-radius:.375rem;font-size:1rem}.mission-closing{font-style:italic;color:#6b7280;margin:2rem 0;text-align:center;font-size:1.1rem}.mission-cta{text-align:center;margin-top:2rem}.btn-mission{padding:1rem 2rem;font-size:1.1rem;border-radius:.75rem;background:linear-gradient(135deg,#10a37f,#0d8c6d);border:none;color:#fff;font-weight:600;transition:all .3s ease}.btn-mission:hover:not(:disabled){transform:translateY(-2px);box-shadow:0 10px 25px #10a37f4d}.about-section{padding:4rem 0;background:#f8fafc}.about-content{max-width:600px;margin:0 auto}.about-content p{font-size:1.1rem;margin-bottom:2rem}@media print{.no-print{display:none!important}.chat-container,.exam-generator,.upload-area{box-shadow:none;border:1px solid #ccc}body{background:#fff;color:#000}}:root{--sidebar-width: 280px;--sidebar-collapsed-width: 0px;--header-height: 80px;--chat-input-height: 120px;--toggle-btn-size: 44px}.main-app{display:flex;height:100vh;overflow:hidden;position:relative}.sidebar-toggle-btn{position:fixed;left:8px;top:20px;width:var(--toggle-btn-size);height:var(--toggle-btn-size);border-radius:50%;border:none;background:#202123;color:#fff;font-size:16px;cursor:pointer;z-index:1100;display:flex;align-items:center;justify-content:center;box-shadow:0 2px 8px #0000004d;transition:all .3s ease}.sidebar-toggle-btn:hover{background:#343541;transform:scale(1.05)}.chatgpt-sidebar{position:fixed;left:0;top:0;width:var(--sidebar-width);height:100vh;background:#202123;color:#fff;display:flex;flex-direction:column;z-index:1000;border-right:1px solid #343541;transition:transform .3s ease,width .3s ease;overflow-y:auto}.chatgpt-sidebar.collapsed{transform:translate(-100%);width:var(--sidebar-collapsed-width)}.main-workspace{flex:1;margin-left:var(--sidebar-width);display:flex;flex-direction:column;height:100vh;transition:margin-left .3s ease;background:#fff}.main-workspace.sidebar-collapsed{margin-left:var(--sidebar-collapsed-width)}.workspace-header{position:fixed;top:0;left:var(--sidebar-width);right:0;height:var(--header-height);background:#fff;border-bottom:1px solid var(--border-color);display:flex;align-items:center;justify-content:space-between;padding:0 1.5rem;z-index:900;transition:left .3s ease;box-shadow:0 2px 4px #0000001a}.main-workspace.sidebar-collapsed .workspace-header{left:var(--sidebar-collapsed-width)}.grade-subject-selector{display:flex;align-items:center;gap:1rem;flex:1}.grade-subject-form{display:flex;align-items:center;gap:.75rem}.grade-subject-form select{min-width:140px;padding:.5rem;border:1px solid var(--border-color);border-radius:var(--border-radius-md);background:#fff}.grade-subject-display .grade-subject-pill{background:var(--primary-color);color:#fff;padding:.5rem 1rem;border-radius:20px;display:flex;align-items:center;gap:.5rem;font-weight:500}.language-toggle{display:flex;background:var(--background-color);border-radius:var(--border-radius-md);padding:2px}.lang-btn{padding:.5rem 1rem;border:none;background:transparent;border-radius:var(--border-radius-sm);cursor:pointer;transition:all .2s ease;font-size:.9rem}.lang-btn.active{background:var(--primary-color);color:#fff}.chat-interface{flex:1;display:flex;flex-direction:column;margin-top:var(--header-height);height:calc(100vh - var(--header-height))}.chat-container{flex:1;display:flex;flex-direction:column;height:100%;padding-bottom:var(--chat-input-height)}.chat-messages{flex:1;overflow-y:auto;padding:1.5rem;display:flex;flex-direction:column;gap:1rem}.chat-input-container{position:relative;bottom:auto;left:auto;right:auto;background:#fff;border-top:1px solid var(--border-color);padding:1rem 1.5rem;z-index:950;transition:left .3s ease;box-shadow:0 -2px 4px #0000001a}.main-workspace.sidebar-collapsed .chat-input-container{left:var(--sidebar-collapsed-width)}.chat-input-form{display:flex;align-items:center;gap:.75rem;width:100%}.chat-input{flex:1;min-height:48px;max-height:120px;padding:.75rem;border:1px solid var(--border-color);border-radius:var(--border-radius-md);resize:none;font-family:inherit;line-height:1.4}.send-btn{width:48px;height:48px;border-radius:50%;border:none;background:var(--primary-color);color:#fff;display:flex;align-items:center;justify-content:center;cursor:pointer;flex-shrink:0;transition:all .2s ease}.send-btn:hover:not(:disabled){background:var(--primary-dark);transform:scale(1.05)}.send-btn:disabled{background:var(--text-muted);cursor:not-allowed;transform:none}.file-upload-area{display:flex;align-items:center;gap:1rem;margin-bottom:.75rem}.file-upload-btn{padding:.5rem 1rem;border:1px solid var(--border-color);border-radius:var(--border-radius-md);background:var(--background-color);cursor:pointer;transition:all .2s ease;font-size:.9rem}.file-upload-btn:hover{background:var(--primary-light);color:#fff;border-color:var(--primary-light)}.sidebar-nav{padding:1rem;border-bottom:1px solid #343541}.nav-btn{width:100%;padding:.75rem;margin-bottom:.5rem;border:none;background:transparent;color:#fff;text-align:left;border-radius:var(--border-radius-md);cursor:pointer;display:flex;align-items:center;gap:.75rem;transition:all .2s ease}.nav-btn:hover,.nav-btn.active{background:#343541}.nav-icon{font-size:1.2rem;width:20px;display:flex;justify-content:center}.conversation-section{flex:1;padding:1rem;overflow-y:auto}.section-header{color:var(--text-muted);font-size:.9rem;margin-bottom:1rem;padding:0 .5rem}.sidebar-bottom{padding:1rem;border-top:1px solid #343541;margin-top:auto}.sidebar-user{display:flex;align-items:center;gap:.75rem;margin-bottom:1rem;padding:.5rem;border-radius:var(--border-radius-md);background:#ffffff0d}.user-avatar{width:32px;height:32px;border-radius:50%;background:var(--primary-color);display:flex;align-items:center;justify-content:center;color:#fff;font-weight:700}.sidebar-logout{width:100%;padding:.75rem;border:none;background:#dc3545;color:#fff;border-radius:var(--border-radius-md);cursor:pointer;transition:all .2s ease}.sidebar-logout:hover{background:#c82333}@media (max-width: 768px){:root{--sidebar-width: 280px;--header-height: 70px;--chat-input-height: 110px;--toggle-btn-size: 40px}.sidebar-toggle-btn{left:6px;top:15px;width:var(--toggle-btn-size);height:var(--toggle-btn-size)}.workspace-header{padding:0 1rem;height:var(--header-height)}.grade-subject-form{flex-wrap:wrap;gap:.5rem}.grade-subject-form select{min-width:120px;font-size:.9rem}.language-toggle{margin-left:auto}.lang-btn{padding:.4rem .8rem;font-size:.85rem}.chat-messages{padding:1rem}.chat-input-container{padding:.75rem 1rem}.chat-input{font-size:16px}.message{max-width:85%}.message-bubble{padding:.75rem;font-size:.95rem;line-height:1.4}}@media (max-width: 480px){:root{--sidebar-width: 260px;--header-height: 65px;--toggle-btn-size: 36px}.workspace-header{padding:0 .75rem}.grade-subject-form select{min-width:100px;font-size:.85rem}.chat-messages{padding:.75rem}.chat-input-container{padding:.5rem .75rem}.message{max-width:90%}.message-bubble{padding:.6rem;font-size:.9rem}}@media (min-width: 769px){.main-workspace{margin-left:var(--sidebar-width)}.workspace-header,.chat-input-container{left:var(--sidebar-width)}.main-workspace.sidebar-collapsed{margin-left:var(--sidebar-collapsed-width)}.main-workspace.sidebar-collapsed .workspace-header,.main-workspace.sidebar-collapsed .chat-input-container{left:var(--sidebar-collapsed-width)}.chat-container{max-width:none;padding:0 2rem;margin:0 auto;width:100%}}@media (max-width: 768px){.app-container .main-workspace.sidebar-collapsed{margin-left:0!important}.app-container .main-workspace.sidebar-collapsed .chat-input-container{left:0!important;right:0!important;width:100vw!important;margin-left:0!important;margin-right:0!important}.app-container .main-workspace.sidebar-collapsed .workspace-header,.app-container .main-workspace .chat-input-container{left:0!important;right:0!important;width:100vw!important}.chat-input-container{padding:8px 12px!important;flex-direction:column!important;align-items:stretch!important;gap:8px!important}.chat-input-form{gap:8px!important;width:100%!important;flex-direction:row!important;align-items:center!important}.chat-input{flex:1!important;min-width:0!important}.file-upload-area{width:100%!important;margin-bottom:0!important}.file-upload-btn{padding:8px 12px!important;font-size:14px!important;min-width:auto!important;white-space:nowrap!important}.send-btn{padding:8px 12px!important;min-width:44px!important;width:44px!important;height:44px!important}}@media screen and (min-width: 1200px){.app-container .main-workspace .chat-container{margin-top:var(--header-height)!important;margin-bottom:0!important;padding:2rem 3rem!important;height:auto!important;min-height:calc(100vh - var(--header-height) - 200px)!important;overflow:visible!important}.app-container .main-workspace .chat-input-container{position:relative!important;left:auto!important;right:auto!important;bottom:auto!important;width:auto!important;padding:18px 28px!important;display:flex!important;flex-direction:column!important;gap:12px!important;align-items:stretch!important;z-index:1!important;box-shadow:none!important}.app-container .main-workspace .chat-input-container .file-upload-area{display:flex!important;align-items:center!important;gap:1rem!important;flex-wrap:nowrap!important;margin-bottom:0!important}.app-container .main-workspace .chat-input-container .file-upload-btn{padding:10px 14px!important;font-size:16px!important;border-radius:10px!important}.app-container .main-workspace .chat-input-form{display:flex!important;gap:12px!important;align-items:center!important;width:100%!important}.app-container .main-workspace .chat-input-form .chat-input{flex:1!important;min-height:56px!important;max-height:260px!important;padding:14px 18px!important;border-radius:12px!important;font-size:18px!important;background:var(--input-background, #fff)!important}.app-container .main-workspace .chat-input-form .send-btn{width:56px!important;height:56px!important;border-radius:12px!important;font-size:20px!important;flex-shrink:0!important}.app-container .main-workspace.sidebar-collapsed .chat-input-container{margin-left:0!important;margin-right:0!important}.app-container .main-workspace .welcome-message{margin-bottom:1.5rem!important}}