* { margin: 0; padding: 0; box-sizing: border-box; }
:root {
  --primary: #4f46e5;
  --primary-light: #eef2ff;
  --primary-dark: #3730a3;
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-400: #9ca3af;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-800: #1f2937;
  --gray-900: #111827;
  --success: #059669;
  --success-light: #ecfdf5;
  --danger: #dc2626;
  --danger-light: #fef2f2;
  --warning: #d97706;
  --warning-light: #fffbeb;
  --bg: #f9fafb;
  --surface: #ffffff;
  --surface-alt: #f3f4f6;
  --text: #1f2937;
  --text-secondary: #6b7280;
  --border: #e5e7eb;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,.1),0 1px 2px rgba(0,0,0,.06);
  --shadow-lg: 0 10px 15px -3px rgba(0,0,0,.1),0 4px 6px -4px rgba(0,0,0,.1);
  --transition: all .2s ease;
}
[data-theme="dark"] {
  --primary: #818cf8;
  --primary-light: #1e1b4b;
  --primary-dark: #a5b4fc;
  --gray-50: #0f172a;
  --gray-100: #1e293b;
  --gray-200: #334155;
  --gray-300: #475569;
  --gray-400: #64748b;
  --gray-500: #94a3b8;
  --gray-600: #cbd5e1;
  --gray-700: #e2e8f0;
  --gray-800: #f1f5f9;
  --gray-900: #f8fafc;
  --success: #34d399;
  --success-light: #064e3b;
  --danger: #f87171;
  --danger-light: #7f1d1d;
  --warning: #fbbf24;
  --warning-light: #78350f;
  --bg: #0f172a;
  --surface: #1e293b;
  --surface-alt: #334155;
  --text: #f1f5f9;
  --text-secondary: #94a3b8;
  --border: #334155;
}
body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif; background: var(--bg); color: var(--text); line-height: 1.6; -webkit-font-smoothing: antialiased; transition: background .2s, color .2s; }
#app { display: flex; min-height: 100vh; }

/* Sidebar */
.sidebar { width: 260px; background: var(--surface); border-right: 1px solid var(--border); display: flex; flex-direction: column; position: fixed; top: 0; left: 0; height: 100vh; z-index: 100; transition: transform .25s ease; }
.sidebar.collapsed { transform: translateX(-220px); }
.sidebar-header { display: flex; align-items: center; gap: 10px; padding: 20px; cursor: pointer; border-bottom: 1px solid var(--border); flex-shrink: 0; }
.sidebar-header .logo { font-size: 28px; }
.sidebar-header h1 { font-size: 16px; font-weight: 700; color: var(--primary); white-space: nowrap; }
.mobile-menu-btn { display: none; position: fixed; top: 12px; left: 12px; z-index: 200; background: var(--surface); border: 1px solid var(--border); border-radius: 8px; padding: 8px 12px; font-size: 20px; cursor: pointer; box-shadow: var(--shadow); }
.sidebar-nav { flex: 1; overflow-y: auto; padding: 12px; }
.nav-section { margin-bottom: 4px; }
.nav-section-title { padding: 8px 12px; font-size: 11px; font-weight: 600; color: var(--text-secondary); text-transform: uppercase; letter-spacing: .5px; }
.nav-item { display: flex; align-items: center; gap: 10px; padding: 10px 12px; border-radius: 8px; cursor: pointer; color: var(--text-secondary); font-size: 14px; transition: var(--transition); }
.nav-item:hover { background: var(--surface-alt); color: var(--text); }
.nav-item.active { background: var(--primary-light); color: var(--primary); font-weight: 600; }
.nav-item .icon { font-size: 18px; width: 24px; text-align: center; flex-shrink: 0; }
.nav-item .badge { margin-left: auto; background: var(--danger); color: #fff; font-size: 11px; padding: 2px 8px; border-radius: 10px; min-width: 20px; text-align: center; }
.sidebar-footer { padding: 12px; border-top: 1px solid var(--border); text-align: right; flex-shrink: 0; }
.btn-icon { background: none; border: 1px solid var(--border); padding: 6px 10px; border-radius: 6px; cursor: pointer; color: var(--text-secondary); font-size: 12px; transition: var(--transition); }
.btn-icon:hover { background: var(--surface-alt); color: var(--text); }

/* Main */
.main-content { flex: 1; margin-left: 260px; padding: 32px; min-height: 100vh; transition: margin-left .25s ease; }
.sidebar.collapsed ~ .main-content { margin-left: 40px; }

/* Animations */
.fade-in { animation: fadeIn .3s ease; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }
.slide-up { animation: slideUp .3s ease; }
@keyframes slideUp { from { opacity: 0; transform: translateY(16px); } to { opacity: 1; transform: translateY(0); } }

/* Skeleton */
.skeleton { display: none; padding: 24px 0; }
.skeleton.active { display: block; }
.skeleton-line { height: 14px; border-radius: 6px; background: linear-gradient(90deg, var(--gray-200) 25%, var(--gray-100) 50%, var(--gray-200) 75%); background-size: 200% 100%; animation: shimmer 1.5s infinite; margin-bottom: 12px; }
.skeleton-line:last-child { width: 45% !important; }
@keyframes shimmer { 0% { background-position: 200% 0; } 100% { background-position: -200% 0; } }

/* Loading */
.loading { display: none; flex-direction: column; align-items: center; justify-content: center; padding: 80px; }
.loading.active { display: flex; }
.spinner { width: 36px; height: 36px; border: 3px solid var(--gray-200); border-top-color: var(--primary); border-radius: 50%; animation: spin .8s linear infinite; }
@keyframes spin { to { transform: rotate(360deg); } }

/* Toast */
#toastContainer { position: fixed; top: 20px; right: 20px; z-index: 999; display: flex; flex-direction: column; gap: 8px; }
.toast { padding: 12px 20px; border-radius: 8px; font-size: 14px; box-shadow: var(--shadow-lg); animation: slideIn .3s ease; max-width: 400px; }
.toast.error { background: var(--danger-light); color: var(--danger); border: 1px solid #fecaca; }
.toast.success { background: var(--success-light); color: var(--success); border: 1px solid #a7f3d0; }
.toast.warning { background: var(--warning-light); color: #92400e; border: 1px solid #fde68a; }
@keyframes slideIn { from { opacity: 0; transform: translateX(40px); } to { opacity: 1; transform: translateX(0); } }

/* Home */
.hero { text-align: center; padding: 32px 20px 24px; }
.hero h2 { font-size: 26px; margin-bottom: 6px; }
.hero p { color: var(--gray-500); font-size: 15px; }
.grade-cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 16px; max-width: 720px; margin: 0 auto 32px; }
.grade-card { padding: 24px; border-radius: var(--radius); background: var(--surface); border: 2px solid var(--border); cursor: pointer; transition: var(--transition); text-align: center; }
.grade-card:hover { border-color: var(--primary); box-shadow: var(--shadow-lg); transform: translateY(-2px); }
.grade-card h3 { font-size: 20px; margin-bottom: 4px; color: var(--text); }
.grade-card p { color: var(--text-secondary); font-size: 13px; }
.quick-actions { max-width: 720px; margin: 0 auto; }
.quick-actions h3 { font-size: 18px; margin-bottom: 16px; }
.action-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr)); gap: 12px; }
.action-card { padding: 20px 16px; background: var(--surface); border-radius: var(--radius); border: 1px solid var(--border); cursor: pointer; text-align: center; transition: var(--transition); }
.action-card:hover { border-color: var(--primary); box-shadow: var(--shadow); transform: translateY(-1px); }
.action-icon { font-size: 28px; display: block; margin-bottom: 8px; }
.action-title { font-weight: 600; font-size: 14px; display: block; margin-bottom: 4px; color: var(--text); }
.action-desc { font-size: 12px; color: var(--text-secondary); }

/* Breadcrumb */
.breadcrumb { display: flex; align-items: center; gap: 8px; font-size: 13px; color: var(--gray-400); margin-bottom: 16px; flex-wrap: wrap; }
.breadcrumb a { color: var(--primary); cursor: pointer; text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }
.breadcrumb span.sep { color: var(--gray-300); }

/* Topic */
.page-topic h2 { font-size: 22px; margin-bottom: 12px; }
.topic-description { color: var(--gray-600); font-size: 15px; margin-bottom: 20px; }
.topic-key-points { background: var(--primary-light); padding: 20px; border-radius: var(--radius); margin-bottom: 20px; }
.topic-key-points h4 { margin-bottom: 12px; color: var(--primary); font-size: 15px; }
.topic-key-points ul { padding-left: 20px; }
.topic-key-points li { margin-bottom: 6px; font-size: 14px; line-height: 1.6; }
.topic-actions { display: flex; gap: 12px; margin-bottom: 24px; flex-wrap: wrap; }
.topic-content { background: #fff; border-radius: var(--radius); padding: 24px; line-height: 1.8; display: none; }
.topic-content.visible { display: block; }
.topic-content h3 { font-size: 18px; margin: 20px 0 12px; color: var(--primary-dark); }
.topic-content h4 { font-size: 15px; margin: 16px 0 8px; }
.topic-content p { margin-bottom: 12px; }
.topic-content ul, .topic-content ol { padding-left: 20px; margin-bottom: 12px; }
.topic-content li { margin-bottom: 6px; }
.topic-content .example-box { background: var(--gray-50); border-left: 4px solid var(--primary); padding: 16px; margin: 16px 0; border-radius: 0 var(--radius) var(--radius) 0; }
.topic-content .katex-display { margin: 12px 0; overflow-x: auto; overflow-y: hidden; }

/* Buttons */
.btn { display: inline-flex; align-items: center; gap: 6px; padding: 10px 20px; border-radius: var(--radius-sm); font-size: 14px; font-weight: 500; cursor: pointer; border: none; transition: var(--transition); }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); transform: translateY(-1px); }
.btn-secondary { background: #fff; color: var(--gray-700); border: 1px solid var(--gray-300); }
.btn-secondary:hover { background: var(--gray-50); border-color: var(--gray-400); }
.btn-success { background: var(--success); color: #fff; }
.btn-success:hover { background: #047857; }
.btn-danger { background: var(--danger); color: #fff; }
.btn-danger:hover { background: #b91c1c; }
.btn-sm { padding: 6px 14px; font-size: 13px; }
.btn:disabled { opacity: .5; cursor: not-allowed; transform: none !important; }

/* Practice */
.practice-setup { background: #fff; padding: 24px; border-radius: var(--radius); margin-bottom: 20px; }
.form-group { margin-bottom: 16px; }
.form-group label { display: block; font-size: 13px; font-weight: 600; color: var(--gray-600); margin-bottom: 6px; }
.form-group select, .form-group textarea { width: 100%; padding: 10px 12px; border: 1px solid var(--gray-300); border-radius: var(--radius-sm); font-size: 14px; background: #fff; color: var(--gray-800); transition: var(--transition); }
.form-group select:focus, .form-group textarea:focus { outline: none; border-color: var(--primary); box-shadow: 0 0 0 3px rgba(79,70,229,.1); }
.problem-card { background: #fff; border-radius: var(--radius); padding: 20px; margin-bottom: 16px; border: 1px solid var(--gray-200); transition: var(--transition); }
.problem-card:hover { box-shadow: var(--shadow); }
.problem-card .problem-header { display: flex; align-items: center; gap: 8px; margin-bottom: 12px; flex-wrap: wrap; }
.problem-card .problem-tag { font-size: 11px; padding: 2px 10px; border-radius: 4px; background: var(--primary-light); color: var(--primary); font-weight: 600; }
.problem-card .problem-question { font-size: 15px; margin-bottom: 12px; line-height: 1.7; }
.problem-card .problem-question .katex { font-size: 1em; }
.problem-card .problem-answer { margin-top: 12px; }
.problem-card .problem-answer textarea { width: 100%; padding: 10px; border: 1px solid var(--gray-300); border-radius: var(--radius-sm); font-size: 14px; min-height: 60px; resize: vertical; transition: var(--transition); }
.problem-card .problem-answer textarea:focus { outline: none; border-color: var(--primary); box-shadow: 0 0 0 3px rgba(79,70,229,.1); }
.problem-result { margin-top: 12px; padding: 16px; border-radius: var(--radius-sm); font-size: 14px; }
.problem-result.correct { background: var(--success-light); border: 1px solid #a7f3d0; }
.problem-result.partial { background: var(--warning-light); border: 1px solid #fde68a; }
.problem-result.wrong { background: var(--danger-light); border: 1px solid #fecaca; }
.problem-result .score { font-weight: 700; font-size: 18px; }
.problem-result .comment { margin-top: 8px; line-height: 1.5; }
.problem-result .solution { margin-top: 12px; padding: 12px; background: rgba(255,255,255,.6); border-radius: 6px; font-size: 13px; line-height: 1.7; }
.total-score { background: var(--primary-light); padding: 16px 20px; border-radius: var(--radius); margin-bottom: 16px; text-align: center; font-size: 18px; font-weight: 600; color: var(--primary); }

/* Mistakes */
.mistake-card { background: #fff; border-radius: var(--radius); padding: 20px; margin-bottom: 16px; border: 1px solid var(--gray-200); }
.mistake-card .mistake-meta { font-size: 12px; color: var(--gray-400); margin-bottom: 8px; }
.mistake-card .mistake-question { font-size: 15px; margin-bottom: 8px; line-height: 1.7; }
.mistake-card .mistake-answer { font-size: 13px; padding: 8px 12px; background: var(--danger-light); border-radius: 6px; margin-bottom: 8px; }
.mistake-card .mistake-solution { font-size: 13px; padding: 8px 12px; background: var(--success-light); border-radius: 6px; }
.mistake-card .mistake-actions { margin-top: 12px; display: flex; gap: 8px; }

/* AI Q&A */
.page-ask .subtitle { color: var(--gray-500); margin-bottom: 20px; }
.qa-context { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 12px; align-items: end; }
.qa-context .form-group { margin-bottom: 0; flex: 1; min-width: 140px; }
.qa-context label { font-size: 12px; }
.qa-context select { font-size: 13px; padding: 8px; }
.qa-input { background: #fff; padding: 20px; border-radius: var(--radius); margin-bottom: 20px; }
.qa-input textarea { width: 100%; padding: 12px; border: 1px solid var(--gray-300); border-radius: var(--radius-sm); font-size: 14px; resize: vertical; margin-bottom: 12px; transition: var(--transition); }
.qa-input textarea:focus { outline: none; border-color: var(--primary); box-shadow: 0 0 0 3px rgba(79,70,229,.1); }
.qa-result { background: #fff; padding: 24px; border-radius: var(--radius); line-height: 1.8; display: none; }
.qa-result.visible { display: block; }
.qa-result h3 { margin-bottom: 12px; font-size: 16px; }
.qa-result .answer-content { white-space: pre-wrap; }
.qa-result .answer-content p { margin-bottom: 10px; }
.qa-result .streaming-cursor::after { content: '▌'; animation: blink 1s step-end infinite; color: var(--primary); }
@keyframes blink { 50% { opacity: 0; } }

/* Records */
.stats-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 12px; margin-bottom: 32px; }
.stat-card { background: #fff; border-radius: var(--radius); padding: 20px 16px; text-align: center; border: 1px solid var(--gray-200); transition: var(--transition); }
.stat-card:hover { box-shadow: var(--shadow); }
.stat-card .stat-number { font-size: 28px; font-weight: 700; color: var(--primary); }
.stat-card .stat-label { font-size: 13px; color: var(--gray-500); margin-top: 4px; }
.study-list, .quiz-list, .mistake-list { margin-bottom: 32px; }
.record-item { background: #fff; border-radius: var(--radius); padding: 16px; margin-bottom: 8px; border: 1px solid var(--gray-200); display: flex; justify-content: space-between; align-items: center; transition: var(--transition); }
.record-item:hover { box-shadow: var(--shadow); }
.record-item .record-info { flex: 1; min-width: 0; }
.record-item .record-title { font-weight: 600; font-size: 14px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.record-item .record-meta { font-size: 12px; color: var(--gray-400); margin-top: 4px; }
.record-item .record-score { font-size: 20px; font-weight: 700; margin-left: 12px; flex-shrink: 0; }

/* Chapter list */
.chapter-list { display: flex; flex-direction: column; gap: 12px; }
.chapter-card { background: #fff; border-radius: var(--radius); padding: 20px; border: 1px solid var(--gray-200); transition: var(--transition); }
.chapter-card:hover { border-color: var(--primary); box-shadow: var(--shadow); }
.chapter-card h3 { font-size: 16px; margin-bottom: 4px; }
.chapter-card p { font-size: 13px; color: var(--gray-500); margin-bottom: 8px; }
.chapter-card .topic-tags { display: flex; flex-wrap: wrap; gap: 6px; }
.chapter-card .topic-tag { font-size: 12px; padding: 3px 12px; border-radius: 12px; background: var(--gray-100); color: var(--gray-600); cursor: pointer; transition: var(--transition); }
.chapter-card .topic-tag:hover { background: var(--primary-light); color: var(--primary); }
.chapter-card .topic-tag.studied { background: #ecfdf5; color: var(--success); }

/* Responsive */
@media (max-width: 768px) {
  .main-content { margin-left: 0; padding: 16px; padding-top: 60px; }
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); box-shadow: var(--shadow-lg); }
  .mobile-menu-btn { display: block; }
  .hero h2 { font-size: 22px; }
  .grade-cards { grid-template-columns: 1fr; }
  .action-grid { grid-template-columns: repeat(2, 1fr); }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .topic-actions { flex-direction: column; }
  .topic-actions .btn { width: 100%; justify-content: center; }
  .problem-card .problem-header { flex-direction: column; align-items: flex-start; }
}

/* Dark theme surface overrides */
[data-theme="dark"] .chapter-card,
[data-theme="dark"] .mistake-card,
[data-theme="dark"] .problem-card,
[data-theme="dark"] .record-item,
[data-theme="dark"] .practice-setup,
[data-theme="dark"] .qa-input,
[data-theme="dark"] .qa-result,
[data-theme="dark"] .topic-content,
[data-theme="dark"] .stat-card,
[data-theme="dark"] .topic-key-points { background: var(--surface); color: var(--text); border-color: var(--border); }
[data-theme="dark"] .form-group select,
[data-theme="dark"] .form-group textarea,
[data-theme="dark"] .qa-input textarea,
[data-theme="dark"] .problem-card .problem-answer textarea { background: var(--surface); color: var(--text); border-color: var(--border); }
[data-theme="dark"] .hero p { color: var(--text-secondary); }
[data-theme="dark"] .breadcrumb { color: var(--text-secondary); }
[data-theme="dark"] .topic-key-points li,
[data-theme="dark"] .topic-content { color: var(--text); }
[data-theme="dark"] .example-box { background: var(--surface-alt); }
[data-theme="dark"] .topic-tag { background: var(--surface-alt); color: var(--text-secondary); }
[data-theme="dark"] .topic-tag.studied { background: rgba(52, 211, 153, .2); color: var(--success); }
[data-theme="dark"] .btn-secondary { background: var(--surface); color: var(--text); border-color: var(--border); }
[data-theme="dark"] .btn-secondary:hover { background: var(--surface-alt); }
[data-theme="dark"] .total-score { background: var(--primary-light); color: var(--primary); }
[data-theme="dark"] .problem-result.solution { color: var(--text); }

/* Modal - generated by JS */