:root{--brand:#1f5cff;--brand-hover:#1749cc;--brand-soft:#eaf0ff;--bg:#ffffff;--surface:#ffffff;--surface-2:#f5f7fb;--border:#e4e9f2;--text:#0e1b33;--muted:#6b7688;--green:#16a86b;--radius:14px;--shadow:0 1px 2px rgba(16,32,64,.04),0 6px 20px rgba(16,32,64,.06)}*{box-sizing:border-box}body,html{margin:0;padding:0;background:var(--bg);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica,Arial,sans-serif;-webkit-font-smoothing:antialiased}a{color:inherit;text-decoration:none}h1,h2,h3{margin:0 0 .3em;line-height:1.2;letter-spacing:-.01em}p{color:var(--muted);line-height:1.6}.container{max-width:1080px;margin:0 auto;padding:28px 24px 60px}.topbar{display:flex;align-items:center;justify-content:space-between;padding:14px 24px;border-bottom:1px solid var(--border);background:#fff;position:-webkit-sticky;position:sticky;top:0;z-index:10}.topbar .brand{font-weight:800;letter-spacing:-.02em;color:var(--brand);font-size:18px}.topbar nav{display:flex;gap:18px;align-items:center}.topbar nav a{color:var(--muted);font-size:14px;font-weight:500}.topbar nav a:hover{color:var(--text)}.btn{display:inline-flex;align-items:center;gap:8px;cursor:pointer;background:var(--brand);color:#fff;border:none;padding:11px 18px;border-radius:10px;font-size:14px;font-weight:600;transition:background .15s,transform .1s;font-family:inherit}.btn:hover{background:var(--brand-hover)}.btn:active{transform:translateY(1px)}.btn:disabled{opacity:.55;cursor:not-allowed}.btn.secondary{background:var(--brand-soft);color:var(--brand)}.btn.secondary:hover{background:#dbe6ff}.btn.ghost{background:transparent;color:var(--muted);padding:7px 12px}.btn.ghost:hover{color:var(--text);background:var(--surface-2)}.btn.green{background:var(--green)}.btn.green:hover{background:#128a58}.btn.small{padding:7px 13px;font-size:13px}.btn.danger{background:transparent;color:#d64545}.btn.danger:hover{background:#fdecec}.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:22px;box-shadow:var(--shadow)}.grid{display:grid;grid-gap:18px;gap:18px;grid-template-columns:repeat(auto-fill,minmax(280px,1fr))}.course-card{display:flex;flex-direction:column;gap:12px;transition:border-color .15s,transform .15s,box-shadow .15s}.course-card:hover{border-color:var(--brand);transform:translateY(-3px);box-shadow:0 10px 30px rgba(31,92,255,.12)}.course-card .meta{font-size:13px;color:var(--muted)}.progress{height:8px;background:var(--surface-2);border-radius:99px;overflow:hidden}.progress>span{display:block;height:100%;background:var(--brand);border-radius:99px;transition:width .3s}label{display:block;font-size:13px;color:var(--text);font-weight:600;margin:14px 0 6px}input,select,textarea{width:100%;padding:11px 13px;border-radius:10px;background:#fff;border:1px solid var(--border);color:var(--text);font-size:14px;font-family:inherit}input:focus,select:focus,textarea:focus{outline:none;border-color:var(--brand);box-shadow:0 0 0 3px var(--brand-soft)}textarea{min-height:90px;resize:vertical}input[type=file]{padding:9px;background:var(--surface-2);cursor:pointer}.error{color:#d64545}.error,.success-msg{font-size:14px;margin-top:10px}.success-msg{color:var(--green)}.hint{color:var(--muted);font-size:13px}.login-wrap{min-height:100vh;display:grid;place-items:center;padding:24px;background:linear-gradient(180deg,var(--brand-soft),#fff 60%)}.login-card{width:100%;max-width:400px}.login-logo{font-weight:800;color:var(--brand);font-size:24px;letter-spacing:-.02em;margin-bottom:6px}.course-layout{display:grid;grid-template-columns:320px 1fr;grid-gap:24px;gap:24px;align-items:start}@media (max-width:860px){.course-layout{grid-template-columns:1fr}}.lesson-list{display:flex;flex-direction:column;gap:4px}.lesson-item{display:flex;align-items:center;gap:10px;padding:11px 12px;border-radius:10px;color:var(--muted);font-size:14px;cursor:pointer;border:1px solid transparent;font-weight:500}.lesson-item:hover{background:var(--surface-2);color:var(--text)}.lesson-item.active{background:var(--brand-soft);color:var(--brand);border-color:transparent;font-weight:600}.lesson-item .check{width:22px;height:22px;border-radius:99px;border:2px solid var(--border);display:grid;place-items:center;flex-shrink:0;font-size:12px;font-weight:700}.lesson-item .check.done{background:var(--green);border-color:var(--green);color:#fff}.video-frame{position:relative;width:100%;padding-top:56.25%;background:#0b1220;border-radius:var(--radius);overflow:hidden;border:1px solid var(--border)}.video-frame iframe,.video-frame video{position:absolute;inset:0;width:100%;height:100%;border:0;background:#000}.video-empty{position:absolute;inset:0;display:grid;place-items:center;color:#94a3b8}.attach{display:flex;align-items:center;gap:10px;padding:11px 14px;border:1px solid var(--border);border-radius:10px;background:var(--surface-2);font-size:14px;font-weight:500}.attach:hover{border-color:var(--brand);color:var(--brand)}table{width:100%;border-collapse:collapse;font-size:14px}td,th{text-align:left;padding:11px 14px;border-bottom:1px solid var(--border)}th{color:var(--muted);font-weight:600;font-size:13px}tr:last-child td{border-bottom:none}.row{gap:12px;flex-wrap:wrap}.row,.spread{display:flex;align-items:center}.spread{justify-content:space-between;gap:16px}.tag{font-size:12px;padding:3px 10px;border-radius:99px;background:var(--surface-2);border:1px solid var(--border);color:var(--muted);font-weight:600}.tag.admin{color:var(--brand);border-color:var(--brand);background:var(--brand-soft)}.stack{display:flex;flex-direction:column;gap:18px}.section-title{font-size:12px;text-transform:uppercase;letter-spacing:.7px;color:var(--muted);font-weight:700;margin:6px 0}.checkbox-row{display:flex;align-items:center;gap:10px;padding:9px 0;font-weight:500}.checkbox-row input{width:auto}.divider{height:1px;background:var(--border);margin:4px 0}