:root{--brand-50: #eef4ff;--brand-100: #dbe6ff;--brand-300: #9db8ff;--brand-500: #4f7cff;--brand-600: #3a63e0;--brand-700: #2d4fbf;--accent-500: #14b8a6;--accent-600: #0d9488;--success: #16a34a;--success-bg: #dcfce7;--warning: #d97706;--warning-bg: #fef3c7;--danger: #dc2626;--danger-bg: #fee2e2;--bg: #f6f8fc;--surface: #ffffff;--surface-2: #f1f5fb;--border: #e3e8f0;--text: #1a2233;--text-muted: #5b6577;--text-faint: #8a93a6;--radius-sm: 8px;--radius: 14px;--radius-lg: 22px;--shadow-sm: 0 1px 2px rgba(16, 24, 40, .06);--shadow: 0 6px 20px rgba(16, 24, 40, .08);--shadow-lg: 0 16px 40px rgba(16, 24, 40, .12);--sidebar-w: 248px;--header-h: 64px;--font: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", sans-serif}*{box-sizing:border-box}html,body,#root{height:100%}body{margin:0;font-family:var(--font);color:var(--text);background:var(--bg);-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility}a{color:var(--brand-600);text-decoration:none}a:hover{text-decoration:underline}h1,h2,h3,h4{margin:0 0 .4em;line-height:1.2;font-weight:700}p{margin:0 0 1em;line-height:1.6}.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;border:1px solid transparent;border-radius:var(--radius);padding:11px 18px;font-size:.95rem;font-weight:600;font-family:inherit;cursor:pointer;transition:transform .06s ease,background .15s ease,box-shadow .15s ease;white-space:nowrap}.btn:active{transform:translateY(1px)}.btn:disabled{opacity:.55;cursor:not-allowed}.btn-primary{background:var(--brand-500);color:#fff;box-shadow:var(--shadow-sm)}.btn-primary:hover:not(:disabled){background:var(--brand-600)}.btn-secondary{background:var(--surface);color:var(--text);border-color:var(--border)}.btn-secondary:hover:not(:disabled){background:var(--surface-2)}.btn-ghost{background:transparent;color:var(--text-muted)}.btn-ghost:hover:not(:disabled){background:var(--surface-2)}.btn-block{width:100%}.btn-lg{padding:14px 22px;font-size:1.05rem}.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-lg);box-shadow:var(--shadow-sm);padding:22px}.field{margin-bottom:16px}.field label{display:block;font-size:.85rem;font-weight:600;color:var(--text-muted);margin-bottom:6px}.input,.select{width:100%;padding:12px 14px;font-size:1rem;font-family:inherit;color:var(--text);background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);outline:none;transition:border-color .15s ease,box-shadow .15s ease}.input:focus,.select:focus{border-color:var(--brand-300);box-shadow:0 0 0 3px var(--brand-50)}.alert{padding:12px 14px;border-radius:var(--radius);font-size:.9rem;margin-bottom:16px}.alert-error{background:var(--danger-bg);color:var(--danger)}.alert-success{background:var(--success-bg);color:var(--success)}.badge{display:inline-flex;align-items:center;gap:6px;padding:4px 10px;border-radius:999px;font-size:.78rem;font-weight:600;background:var(--brand-50);color:var(--brand-700)}.muted{color:var(--text-muted)}.faint{color:var(--text-faint)}.center{text-align:center}.row{display:flex;align-items:center}.gap-8{gap:8px}.gap-12{gap:12px}.gap-16{gap:16px}.stack>*+*{margin-top:16px}.spread{justify-content:space-between}.grow{flex:1}.auth-wrap{min-height:100vh;display:grid;place-items:center;padding:24px;background:radial-gradient(1200px 500px at 100% -10%,var(--brand-100),transparent),radial-gradient(900px 500px at -10% 110%,#d6faf4,transparent),var(--bg)}.auth-card{width:100%;max-width:420px}.brand-mark{display:inline-flex;align-items:center;gap:10px;font-weight:800;font-size:1.15rem}.brand-logo{width:34px;height:34px;border-radius:10px;background:linear-gradient(135deg,var(--brand-500),var(--accent-500));display:grid;place-items:center;color:#fff;font-size:1.1rem}.app-shell{min-height:100vh;display:flex}.sidebar{width:var(--sidebar-w);flex-shrink:0;background:var(--surface);border-right:1px solid var(--border);padding:18px 14px;display:flex;flex-direction:column;gap:6px;position:sticky;top:0;height:100vh}.nav-link{display:flex;align-items:center;gap:12px;padding:11px 14px;border-radius:var(--radius);color:var(--text-muted);font-weight:600;font-size:.95rem}.nav-link:hover{background:var(--surface-2);text-decoration:none;color:var(--text)}.nav-link.active{background:var(--brand-50);color:var(--brand-700)}.nav-icon{font-size:1.15rem;width:22px;text-align:center}.app-main{flex:1;min-width:0;display:flex;flex-direction:column}.app-header{height:var(--header-h);display:flex;align-items:center;justify-content:space-between;gap:16px;padding:0 22px;background:var(--surface);border-bottom:1px solid var(--border);position:sticky;top:0;z-index:20}.app-content{padding:26px;max-width:1080px;width:100%;margin:0 auto}.avatar{width:36px;height:36px;border-radius:50%;background:var(--brand-500);color:#fff;display:grid;place-items:center;font-weight:700;font-size:.9rem}.icon-btn{display:none;background:transparent;border:none;font-size:1.5rem;cursor:pointer;color:var(--text)}.backdrop{display:none}@media (max-width: 820px){.icon-btn{display:inline-flex}.sidebar{position:fixed;z-index:40;left:0;top:0;transform:translate(-100%);transition:transform .22s ease;box-shadow:var(--shadow-lg)}.sidebar.open{transform:translate(0)}.backdrop.show{display:block;position:fixed;top:0;right:0;bottom:0;left:0;background:#10182866;z-index:30}.app-content{padding:18px}}.spinner{width:22px;height:22px;border:3px solid var(--brand-100);border-top-color:var(--brand-500);border-radius:50%;animation:spin .8s linear infinite}.page-loader{min-height:60vh;display:grid;place-items:center}@keyframes spin{to{transform:rotate(360deg)}}@keyframes fadeInUp{0%{opacity:0;transform:translateY(8px)}to{opacity:1;transform:translateY(0)}}.fade-in{animation:fadeInUp .25s ease both}.call-layout{display:grid;grid-template-columns:300px 1fr;gap:18px;align-items:start}.call-videos{display:flex;flex-direction:column;gap:12px;position:sticky;top:84px}.video-tile{position:relative;background:#0d1220;border-radius:var(--radius);overflow:hidden;aspect-ratio:4 / 3}.video-tile video{width:100%;height:100%;object-fit:cover}.video-tile .tile-empty{position:absolute;top:0;right:0;bottom:0;left:0;display:grid;place-items:center}.video-tile .tile-label{position:absolute;left:8px;bottom:8px;background:#0000008c;color:#fff;padding:2px 10px;border-radius:999px;font-size:.78rem}.call-board{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius-lg);padding:24px;min-height:380px}@media (max-width: 900px){.call-layout{grid-template-columns:1fr}.call-videos{position:static;flex-direction:row}.video-tile{flex:1}}.teacher-stage{display:grid;grid-template-columns:340px 1fr;gap:22px;align-items:start}.teacher-stage .avatar-col{position:sticky;top:84px}.avatar-canvas{width:100%;border-radius:var(--radius-lg);overflow:hidden;background:radial-gradient(circle at 50% 30%,#eef4ff,#dbe6ff 60%,#cdd9f7);border:1px solid var(--border)}@media (max-width: 860px){.teacher-stage{grid-template-columns:1fr}.teacher-stage .avatar-col{position:static}}@keyframes recPulse{0%{box-shadow:0 0 #dc262673}70%{box-shadow:0 0 0 16px #dc262600}to{box-shadow:0 0 #dc262600}}.record-btn.is-recording{animation:recPulse 1.4s ease-out infinite}.record-btn:active{transform:scale(.96)}