:root{
  --bg:#0b1220; --panel:#07101a; --muted:#9aa7b7; --accent:#06b6d4; --accent-2:#7c3aed; --card:rgba(255,255,255,0.03); --text:#e6eef8;
}
*{box-sizing:border-box}
html,body{height:100%;margin:0;font-family:Inter, ui-sans-serif, system-ui, -apple-system,'Segoe UI',Roboto,'Helvetica Neue',Arial}
body{background:linear-gradient(180deg,#05112b 0%, #071228 100%);color:var(--text);display:flex;flex-direction:column;min-height:100vh}
.site-header{display:flex;justify-content:space-between;align-items:center;padding:14px 22px}
.brand{display:flex;gap:12px;align-items:center}
.brand h1{font-size:18px;margin:0}
.tag{margin:0;color:var(--muted);font-size:12px}
.actions{display:flex;gap:10px;align-items:center}
.icon-btn{background:transparent;border:1px solid rgba(255,255,255,0.04);padding:8px;border-radius:8px;color:var(--text);cursor:pointer}
.btn{border:none;padding:8px 12px;border-radius:8px;background:linear-gradient(90deg,var(--accent),var(--accent-2));color:#041426;cursor:pointer;font-weight:700}
.btn.ghost{background:transparent;border:1px solid rgba(255,255,255,0.04);color:var(--text)}
.btn.small{padding:6px 10px;background:rgba(255,255,255,0.02);border:1px solid rgba(255,255,255,0.03)}
.main{display:flex;gap:18px;padding:18px;flex:1;align-items:flex-start}
.sidebar{width:280px;background:var(--card);backdrop-filter: blur(6px);border-radius:12px;padding:14px;box-shadow:0 8px 24px rgba(2,6,23,0.6)}
.lesson-list{display:flex;flex-direction:column;gap:8px;max-height:66vh;overflow:auto;margin-top:8px}
.lesson-list button{background:transparent;border:1px solid rgba(255,255,255,0.03);padding:10px;border-radius:10px;color:var(--text);text-align:left;cursor:pointer}
.lesson-list button.active{border-color:var(--accent);box-shadow:0 8px 20px rgba(6,182,212,0.06);background:linear-gradient(180deg, rgba(6,182,212,0.04), transparent)}
.nav-mini{display:flex;gap:8px;justify-content:center;margin-top:12px}
.content{flex:1;background:linear-gradient(180deg, rgba(255,255,255,0.02), transparent);padding:20px;border-radius:12px;min-height:60vh;box-shadow:0 10px 34px rgba(2,6,23,0.5)}
.content-head{display:flex;flex-direction:column;gap:6px}
.label{display:block;margin:12px 0 6px;color:var(--muted);font-size:13px}
textarea#editor{width:100%;height:260px;border-radius:10px;border:1px solid rgba(255,255,255,0.04);padding:12px;background:#031026;color:#dfffe2;font-family:ui-monospace,SFMono-Regular,Menlo,Monaco,'Roboto Mono',monospace;font-size:13px;white-space:pre-wrap}
.controls{display:flex;gap:10px;align-items:center;margin-top:10px}
.status{margin-left:auto;color:var(--muted);font-size:13px}
.output{background:#021124;padding:12px;border-radius:8px;border:1px solid rgba(255,255,255,0.03);min-height:120px;color:#9be7ff;white-space:pre-wrap;margin-top:8px}
.muted{color:var(--muted)}
.about{margin-top:12px;color:var(--muted)}
.footer{padding:12px 18px;text-align:center;color:var(--muted);font-size:13px}
body.light{--bg:#f7fafc;--panel:#ffffff;--muted:#6b7280;--accent:#0ea5ff;--accent-2:#7c3aed;--text:#0b1220;--card:rgba(2,6,23,0.02);background:linear-gradient(180deg,#f8fafc 0%, #eef2ff 100%)}
body.light textarea#editor{background:#fff;color:#222;border-color:#ddd}
@media (max-width:900px){.main{flex-direction:column}.sidebar{width:100%}}