:root{--color-bg:#f4f5f9;--color-surface:#fff;--color-surface-alt:#f9fafb;--color-border:#e5e7eb;--color-text:#1f2330;--color-text-muted:#6b7280;--color-primary:#4f46e5;--color-primary-hover:#4338ca;--color-primary-soft:#eef2ff;--color-success:#16a34a;--color-success-soft:#dcfce7;--color-warning:#d97706;--color-warning-soft:#fef3c7;--color-danger:#dc2626;--color-danger-soft:#fee2e2;--color-info:#0891b2;--color-info-soft:#cffafe;--shadow-sm:0 1px 2px #1018280f;--shadow-md:0 4px 12px #10182814;--shadow-lg:0 12px 32px #10182824;--radius-sm:8px;--radius-md:12px;--radius-lg:18px;--sidebar-width:250px;--topbar-height:64px}:root[data-theme=dark]{--color-bg:#10121a;--color-surface:#171a25;--color-surface-alt:#1e2230;--color-border:#2a2f40;--color-text:#e7e9f2;--color-text-muted:#9aa1b5;--color-primary:#818cf8;--color-primary-hover:#6366f1;--color-primary-soft:#23253c;--color-success:#4ade80;--color-success-soft:#163524;--color-warning:#fbbf24;--color-warning-soft:#3a2e10;--color-danger:#f87171;--color-danger-soft:#3a1c1e;--color-info:#22d3ee;--color-info-soft:#123640;--shadow-sm:0 1px 2px #0006;--shadow-md:0 4px 14px #00000073;--shadow-lg:0 16px 36px #0000008c}*{box-sizing:border-box}html,body,#root{height:100%}body{background:var(--color-bg);color:var(--color-text);-webkit-font-smoothing:antialiased;margin:0;font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Arial,sans-serif;transition:background-color .2s,color 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12px;font-size:.92rem;font-weight:500;display:flex}.nav-link:hover{background:var(--color-surface-alt);color:var(--color-text)}.nav-link.active{background:var(--color-primary-soft);color:var(--color-primary);font-weight:600}.main-area{margin-left:var(--sidebar-width);flex-direction:column;flex:1;min-width:0;display:flex}.topbar{height:var(--topbar-height);border-bottom:1px solid var(--color-border);background:var(--color-surface);z-index:30;justify-content:space-between;align-items:center;gap:12px;padding:0 24px;display:flex;position:sticky;top:0}.topbar-title{font-size:1.05rem;font-weight:600}.icon-btn{border:1px solid var(--color-border);background:var(--color-surface-alt);width:38px;height:38px;color:var(--color-text);cursor:pointer;border-radius:50%;justify-content:center;align-items:center;font-size:1rem;display:flex;position:relative}.icon-btn:hover{background:var(--color-primary-soft)}.badge-dot{background:var(--color-danger);color:#fff;border-radius:999px;justify-content:center;align-items:center;min-width:16px;height:16px;padding:0 4px;font-size:.62rem;font-weight:700;display:flex;position:absolute;top:-2px;right:-2px}.page-content{flex:1;width:100%;max-width:1280px;margin:0 auto;padding:24px}.mobile-menu-btn{display:none}@media (width<=960px){.sidebar{transform:translate(-100%)}.sidebar.open{box-shadow:var(--shadow-lg);transform:translate(0)}.main-area{margin-left:0}.mobile-menu-btn{display:flex}.page-content{padding:16px}}.auth-page{background:linear-gradient(160deg, var(--color-primary-soft), var(--color-bg) 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var(--color-primary-soft)}textarea.input{resize:vertical;min-height:80px}.field-error{color:var(--color-danger);margin-top:5px;font-size:.78rem}.row-2{grid-template-columns:1fr 1fr;gap:12px;display:grid}@media (width<=520px){.row-2{grid-template-columns:1fr}}.btn{border-radius:var(--radius-sm);cursor:pointer;border:none;justify-content:center;align-items:center;gap:8px;padding:10px 16px;font-size:.88rem;font-weight:600;transition:transform .1s,background-color .15s,opacity .15s;display:inline-flex}.btn:active{transform:translateY(1px)}.btn:disabled{opacity:.55;cursor:not-allowed}.btn-primary{background:var(--color-primary);color:#fff}.btn-primary:hover:not(:disabled){background:var(--color-primary-hover)}.btn-secondary{background:var(--color-surface-alt);color:var(--color-text);border:1px solid var(--color-border)}.btn-secondary:hover:not(:disabled){background:var(--color-border)}.btn-danger{background:var(--color-danger-soft);color:var(--color-danger)}.btn-danger:hover:not(:disabled){filter:brightness(.95)}.btn-success{background:var(--color-success);color:#fff}.btn-block{width:100%}.btn-sm{padding:6px 12px;font-size:.78rem}.btn-icon{border-radius:50%;padding:8px}.card{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius-md);box-shadow:var(--shadow-sm);padding:20px}.card-title{margin-bottom:14px;font-size:1rem;font-weight:700}.stat-grid{grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:16px;margin-bottom:20px;display:grid}.stat-card{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius-md);box-shadow:var(--shadow-sm);flex-direction:column;gap:6px;padding:18px 20px;display:flex}.stat-card .stat-label{color:var(--color-text-muted);font-size:.8rem;font-weight:600}.stat-card 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.3s}.table-wrap{overflow-x:auto}table.data-table{border-collapse:collapse;width:100%;font-size:.88rem}table.data-table th{text-align:left;color:var(--color-text-muted);border-bottom:1px solid var(--color-border);white-space:nowrap;padding:10px 12px;font-weight:600}table.data-table td{border-bottom:1px solid var(--color-border);vertical-align:middle;padding:12px}table.data-table tr:last-child td{border-bottom:none}table.data-table tr:hover td{background:var(--color-surface-alt)}.tabs{gap:6px;margin-bottom:18px;padding-bottom:4px;display:flex;overflow-x:auto}.tab-btn{border:1px solid var(--color-border);background:var(--color-surface);color:var(--color-text-muted);white-space:nowrap;cursor:pointer;border-radius:999px;padding:8px 16px;font-size:.84rem;font-weight:600}.tab-btn.active{background:var(--color-primary);color:#fff;border-color:var(--color-primary)}.task-item{border:1px solid var(--color-border);border-radius:var(--radius-md);background:var(--color-surface);flex-direction:column;gap:10px;margin-bottom:12px;padding:14px 16px;display:flex}.task-item.completed{border-color:var(--color-success);background:var(--color-success-soft)}.task-header{flex-wrap:wrap;justify-content:space-between;align-items:flex-start;gap:10px;display:flex}.task-subject{font-size:.95rem;font-weight:700}.task-meta{color:var(--color-text-muted);font-size:.8rem}.task-actions{flex-wrap:wrap;gap:8px;display:flex}.checkbox-toggle{cursor:pointer;align-items:center;gap:8px;font-size:.85rem;font-weight:600;display:flex}.checkbox-toggle input{width:18px;height:18px;accent-color:var(--color-success)}.video-links{flex-wrap:wrap;gap:8px;display:flex}.video-chip{background:var(--color-info-soft);color:var(--color-info);border-radius:999px;padding:4px 10px;font-size:.76rem;font-weight:600}.assignment-chip{background:var(--color-primary-soft);color:var(--color-primary);border-radius:999px;padding:4px 10px;font-size:.76rem;font-weight:600}.question-card{border:1px solid var(--color-border);border-radius:var(--radius-md);background:var(--color-surface);cursor:pointer;flex-direction:column;gap:8px;margin-bottom:12px;padding:16px;transition:box-shadow .15s;display:flex}.question-card:hover{box-shadow:var(--shadow-md)}.chat-window{flex-direction:column;height:460px;display:flex}.chat-messages{flex-direction:column;flex:1;gap:10px;padding:16px;display:flex;overflow-y:auto}.chat-bubble{background:var(--color-surface-alt);border:1px solid var(--color-border);border-radius:14px;align-self:flex-start;max-width:78%;padding:10px 14px;font-size:.87rem}.chat-bubble.mine{background:var(--color-primary);color:#fff;border:none;align-self:flex-end}.chat-bubble.solution{border:1px solid var(--color-success)}.chat-bubble img{object-fit:cover;border-radius:10px;max-height:220px;margin-top:6px}.chat-meta{opacity:.7;margin-top:4px;font-size:.68rem}.chat-input-bar{border-top:1px solid var(--color-border);gap:8px;padding:12px;display:flex}.modal-overlay{z-index:100;background:#0f111a80;justify-content:center;align-items:center;padding:16px;display:flex;position:fixed;inset:0}.modal-box{background:var(--color-surface);border-radius:var(--radius-lg);width:100%;max-width:520px;max-height:90vh;box-shadow:var(--shadow-lg);border:1px solid var(--color-border);padding:24px;overflow-y:auto}.modal-header{justify-content:space-between;align-items:center;margin-bottom:18px;display:flex}.modal-title{font-size:1.05rem;font-weight:700}.flex{display:flex}.flex-between{justify-content:space-between;align-items:center;display:flex}.flex-col{flex-direction:column;display:flex}.gap-8{gap:8px}.gap-12{gap:12px}.gap-16{gap:16px}.muted{color:var(--color-text-muted)}.text-sm{font-size:.85rem}.mt-8{margin-top:8px}.mt-16{margin-top:16px}.mt-24{margin-top:24px}.mb-8{margin-bottom:8px}.mb-16{margin-bottom:16px}.empty-state{text-align:center;color:var(--color-text-muted);padding:50px 20px}.spinner{border:3px solid var(--color-border);border-top-color:var(--color-primary);border-radius:50%;width:24px;height:24px;animation:.7s linear infinite spin}@keyframes spin{to{transform:rotate(360deg)}}.center-page{justify-content:center;align-items:center;min-height:60vh;display:flex}.avatar{background:var(--color-primary-soft);width:36px;height:36px;color:var(--color-primary);border-radius:50%;flex-shrink:0;justify-content:center;align-items:center;font-size:.85rem;font-weight:700;display:flex;overflow:hidden}.section-header{flex-wrap:wrap;justify-content:space-between;align-items:center;gap:10px;margin-bottom:16px;display:flex}.section-title{font-size:1.2rem;font-weight:700}.grid-2{grid-template-columns:1.4fr 1fr;gap:20px;display:grid}@media (width<=960px){.grid-2{grid-template-columns:1fr}}.chip-select{flex-wrap:wrap;gap:8px;display:flex}.chip-option{border:1px solid var(--color-border);background:var(--color-surface);cursor:pointer;color:var(--color-text-muted);border-radius:999px;padding:8px 14px;font-size:.82rem;font-weight:600}.chip-option.selected{background:var(--color-primary);border-color:var(--color-primary);color:#fff}.alert{border-radius:var(--radius-sm);margin-bottom:14px;padding:12px 14px;font-size:.85rem}.alert-danger{background:var(--color-danger-soft);color:var(--color-danger)}.alert-success{background:var(--color-success-soft);color:var(--color-success)}