*,:before,:after{box-sizing:border-box;margin:0;padding:0}:root{--bg:#fff;--bg-2:#f7f7f8;--bg-3:#efefef;--ink:#111;--ink-2:#555;--ink-3:#888;--border:#e2e2e2;--accent:#7c3aed;--accent-hover:#6d28d9;--accent-light:#ede9fe;--danger:#dc2626;--success:#16a34a;--radius:10px;--shadow:0 1px 4px #00000014}@media (prefers-color-scheme:dark){:root{--bg:#0f0f10;--bg-2:#1a1a1e;--bg-3:#26262c;--ink:#f0f0f0;--ink-2:#aaa;--ink-3:#666;--border:#2e2e36;--accent:#a78bfa;--accent-hover:#8b5cf6;--accent-light:#2d1b6b;--shadow:0 1px 4px #0006}}body{background:var(--bg);color:var(--ink);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,system-ui,sans-serif;font-size:15px;line-height:1.6}a{color:var(--accent);text-decoration:none}a:hover{text-decoration:underline}.shell{flex-direction:column;min-height:100vh;display:flex}nav.topbar{border-bottom:1px solid var(--border);background:var(--bg);z-index:100;align-items:center;gap:12px;height:56px;padding:0 20px;display:flex;position:sticky;top:0}nav.topbar .logo{color:var(--ink);margin-right:auto;font-size:17px;font-weight:700;text-decoration:none}nav.topbar .logo:hover{text-decoration:none}.content{flex:1;width:100%;max-width:1000px;margin:0 auto;padding:32px 20px}.btn{border-radius:var(--radius);cursor:pointer;border:1px solid #0000;align-items:center;gap:6px;padding:8px 16px;font-size:14px;font-weight:500;line-height:1.4;text-decoration:none;transition:background .15s,color .15s;display:inline-flex}.btn:hover{text-decoration:none}.btn-primary{background:var(--accent);color:#fff}.btn-primary:hover{background:var(--accent-hover);color:#fff}.btn-ghost{color:var(--ink-2);border-color:var(--border);background:0 0}.btn-ghost:hover{background:var(--bg-3);color:var(--ink)}.btn-danger{color:var(--danger);border-color:var(--danger);background:0 0}.btn-danger:hover{background:var(--danger);color:#fff}.btn-sm{padding:5px 11px;font-size:13px}.card{background:var(--bg-2);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:20px}.course-grid{grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:20px;display:grid}.course-card{background:var(--bg-2);border:1px solid var(--border);border-radius:var(--radius);color:inherit;flex-direction:column;text-decoration:none;transition:box-shadow .15s;display:flex;overflow:hidden}.course-card:hover{text-decoration:none;box-shadow:0 4px 16px #0000001f}.course-card-cover{aspect-ratio:16/9;background:var(--bg-3);object-fit:cover;width:100%}.course-card-cover-placeholder{aspect-ratio:16/9;background:var(--accent-light);justify-content:center;align-items:center;font-size:40px;display:flex}.course-card-body{flex-direction:column;flex:1;gap:6px;padding:16px;display:flex}.course-card-title{font-size:16px;font-weight:600}.course-card-desc{color:var(--ink-2);flex:1;font-size:13px}.course-card-meta{color:var(--ink-3);font-size:12px}.course-layout{align-items:flex-start;gap:32px;display:flex}.lesson-sidebar{flex-shrink:0;width:260px;max-height:calc(100vh - 90px);position:sticky;top:72px;overflow-y:auto}.lesson-sidebar h3{color:var(--ink-3);text-transform:uppercase;letter-spacing:.05em;margin-bottom:10px;font-size:13px;font-weight:600}.lesson-nav-item{color:var(--ink-2);cursor:pointer;text-align:left;background:0 0;border:none;border-radius:7px;align-items:center;gap:8px;width:100%;padding:8px 12px;font-size:14px;text-decoration:none;transition:background .12s;display:flex}.lesson-nav-item:hover{background:var(--bg-3);color:var(--ink);text-decoration:none}.lesson-nav-item.active{background:var(--accent-light);color:var(--accent);font-weight:500}.lesson-nav-item.done .check{color:var(--success)}.lesson-main{flex:1;min-width:0}.lesson-header{margin-bottom:24px}.lesson-header h1{margin-bottom:6px;font-size:24px;font-weight:700}.lesson-nav-btns{gap:10px;margin-top:16px;display:flex}.prose{color:var(--ink);line-height:1.8}.prose h1,.prose h2,.prose h3{margin-top:1.5em;margin-bottom:.5em;font-weight:600}.prose h1{font-size:1.5em}.prose h2{font-size:1.25em}.prose h3{font-size:1.1em}.prose p{margin-bottom:1em}.prose ul,.prose ol{margin-bottom:1em;padding-left:1.5em}.prose li{margin-bottom:.3em}.prose blockquote{border-left:3px solid var(--accent);color:var(--ink-2);margin:1em 0;padding-left:1em}.prose code{background:var(--bg-3);border-radius:4px;padding:2px 5px;font-family:monospace;font-size:.9em}.prose pre{background:var(--bg-3);border-radius:var(--radius);margin-bottom:1em;padding:14px;overflow-x:auto}.prose pre code{background:0 0;padding:0}.prose img{border-radius:var(--radius);max-width:100%;margin:1em 0}.prose a{color:var(--accent)}.prose hr{border:none;border-top:1px solid var(--border);margin:2em 0}.video-wrap{border-radius:var(--radius);background:#000;margin-bottom:24px;padding-top:56.25%;position:relative;overflow:hidden}.video-wrap iframe{border:none;width:100%;height:100%;position:absolute;inset:0}.assignment-box{background:var(--accent-light);border-left:4px solid var(--accent);border-radius:var(--radius);margin:24px 0;padding:18px 20px}.assignment-box h3{text-transform:uppercase;letter-spacing:.05em;color:var(--accent);margin-bottom:8px;font-size:14px;font-weight:700}.submission-form{flex-direction:column;gap:16px;margin-top:24px;display:flex}.submission-form label{color:var(--ink-2);margin-bottom:6px;font-size:14px;font-weight:600;display:block}textarea.field,input.field{border-radius:var(--radius);border:1px solid var(--border);background:var(--bg);width:100%;color:var(--ink);resize:vertical;padding:12px 14px;font-family:inherit;font-size:14px;transition:border-color .15s}textarea.field:focus,input.field:focus{border-color:var(--accent);outline:none}textarea.field{min-height:140px}.save-status{color:var(--success);font-size:13px}.form-group{flex-direction:column;gap:6px;margin-bottom:16px;display:flex}.form-group label{color:var(--ink-2);font-size:13px;font-weight:600}.checkbox-row{align-items:center;gap:8px;font-size:14px;display:flex}table.data-table{border-collapse:collapse;width:100%;font-size:14px}.data-table th{text-align:left;text-transform:uppercase;letter-spacing:.05em;color:var(--ink-3);border-bottom:1px solid var(--border);padding:10px 12px;font-size:12px}.data-table td{border-bottom:1px solid var(--border);vertical-align:top;padding:10px 12px}.data-table tr:last-child td{border-bottom:none}.data-table tr:hover td{background:var(--bg-2)}.page-header{justify-content:space-between;align-items:center;gap:12px;margin-bottom:28px;display:flex}.page-header h1{font-size:22px;font-weight:700}.page-header p{color:var(--ink-2);margin-top:2px;font-size:14px}.divider{border:none;border-top:1px solid var(--border);margin:24px 0}.badge{border-radius:20px;padding:2px 8px;font-size:12px;font-weight:500;display:inline-block}.badge-green{color:#166534;background:#dcfce7}.badge-gray{background:var(--bg-3);color:var(--ink-3)}.spinner{border:2px solid var(--border);border-top-color:var(--accent);border-radius:50%;width:24px;height:24px;animation:.6s linear infinite spin}@keyframes spin{to{transform:rotate(360deg)}}.loading-center{justify-content:center;padding:60px 0;display:flex}.error-box{color:var(--danger);border-radius:var(--radius);background:#fef2f2;border:1px solid #fecaca;padding:14px 16px;font-size:14px}.empty{text-align:center;color:var(--ink-3);padding:48px 0;font-size:15px}.image-row{flex-wrap:wrap;gap:10px;margin:16px 0;display:flex}.image-thumb{object-fit:cover;border-radius:var(--radius);border:1px solid var(--border);width:160px;height:110px}.image-thumb-admin{display:inline-block;position:relative}.image-thumb-admin .del-img{color:#fff;cursor:pointer;background:#00000080;border:none;border-radius:50%;justify-content:center;align-items:center;width:22px;height:22px;font-size:12px;display:flex;position:absolute;top:4px;right:4px}@media (width<=700px){.course-layout{flex-direction:column}.lesson-sidebar{width:100%;max-height:none;position:static}}