:root { --bg:#14161a; --panel:#1d2026; --line:#2c313a; --text:#e6e8eb; --muted:#9aa3ad; --accent:#5aa9ff; --ok:#4cc38a; --bad:#ff6b6b; }
* { box-sizing: border-box; }
body { margin:0; font:15px/1.5 system-ui, sans-serif; background:var(--bg); color:var(--text); }
header { display:flex; align-items:center; gap:24px; padding:10px 20px; background:var(--panel); border-bottom:1px solid var(--line); }
header h1 { margin:0; font-size:20px; }
nav { display:flex; gap:6px; flex:1; }
.tab { background:none; border:0; color:var(--muted); padding:6px 12px; border-radius:6px; cursor:pointer; font:inherit; }
.tab.active { background:var(--line); color:var(--text); }
#whoami { color:var(--muted); }
#whoami a { color:var(--accent); margin-left:10px; }
.hidden { display:none !important; }
.center { text-align:center; margin-top:80px; }
.btn { background:var(--line); color:var(--text); border:0; padding:8px 14px; border-radius:6px; cursor:pointer; font:inherit; text-decoration:none; display:inline-block; }
.btn.primary { background:var(--accent); color:#06121f; font-weight:600; }
.btn.subtle { background:none; color:var(--muted); }
main { display:flex; min-height:calc(100vh - 52px); }
#sidebar { width:260px; padding:14px; background:var(--panel); border-right:1px solid var(--line); overflow-y:auto; }
#sidebar h3 { margin:16px 0 6px; font-size:12px; text-transform:uppercase; letter-spacing:.06em; color:var(--muted); }
#sidebar .item { display:flex; justify-content:space-between; padding:6px 8px; border-radius:6px; cursor:pointer; }
#sidebar .item:hover { background:var(--line); }
#sidebar .item.current { background:var(--line); outline:1px solid var(--accent); }
#sidebar .item .pts { color:var(--muted); font-size:12px; }
#sidebar .item.done .name::before { content:"\2713  "; color:var(--ok); }
#sidebar .total { color:var(--muted); font-size:13px; }
#workspace, #board { flex:1; padding:18px 24px; min-width:0; }
#lesson h2 { margin:0 0 6px; }
#lesson p { max-width:70ch; }
#lesson code, #results code { background:var(--line); padding:1px 5px; border-radius:4px; font-family:ui-monospace, monospace; }
#editor-row { display:flex; gap:18px; flex-wrap:wrap; margin-top:12px; }
#editor-col { flex:1; min-width:340px; }
#code { width:100%; height:300px; background:#0e1013; color:var(--text); border:1px solid var(--line); border-radius:8px; padding:10px;
  font:14px/1.45 ui-monospace, monospace; tab-size:4; resize:vertical; }
.buttons { display:flex; gap:8px; align-items:center; margin-top:8px; }
#status { color:var(--muted); margin-left:8px; }
#stage { background:white; border-radius:8px; border:1px solid var(--line); max-width:100%; }
#results { margin-top:12px; }
.res { padding:4px 0; }
.res.ok::before { content:"\2713  "; color:var(--ok); }
.res.bad::before { content:"\2717  "; color:var(--bad); }
.banner { padding:10px 14px; border-radius:8px; margin-bottom:6px; }
.banner.ok { background:#12301f; border:1px solid var(--ok); }
.banner.bad { background:#34191a; border:1px solid var(--bad); }
#output { background:#0e1013; border:1px solid var(--line); border-radius:8px; padding:10px; min-height:60px; margin-top:12px; white-space:pre-wrap; }
table { border-collapse:collapse; min-width:420px; }
th, td { text-align:left; padding:8px 14px; border-bottom:1px solid var(--line); }
td.num, th.num { text-align:right; }
tr.me td { color:var(--accent); font-weight:600; }