:root {
  --bg: #0d1117;
  --bg2: #161b22;
  --bg3: #1c2230;
  --line: #262d3a;
  --fg: #e6edf3;
  --muted: #8b949e;
  --accent: #4ee39a;
  --accent2: #58a6ff;
  --amber: #f0b429;
  --red: #ff6b6b;
  --radius: 10px;
  --mono: "JetBrains Mono", "SF Mono", ui-monospace, Consolas, monospace;
  --sans: "Inter", system-ui, -apple-system, "Segoe UI", sans-serif;
}
* { box-sizing: border-box; }
html, body { margin: 0; height: 100%; }
body {
  background: var(--bg);
  color: var(--fg);
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.6;
  display: grid;
  grid-template-columns: 300px 1fr;
  height: 100vh;
  overflow: hidden;
}

/* ---------- sidebar ---------- */
#sidebar {
  background: var(--bg2);
  border-right: 1px solid var(--line);
  overflow-y: auto;
  padding: 0 0 40px;
}
#brand {
  position: sticky; top: 0; z-index: 5;
  background: var(--bg2);
  padding: 18px 20px 14px;
  border-bottom: 1px solid var(--line);
}
#brand h1 { font-size: 18px; margin: 0; letter-spacing: -.3px; }
#brand h1 span { color: var(--accent); }
#brand .tag { color: var(--muted); font-size: 12px; margin-top: 2px; }
#overall { margin-top: 12px; }
.bar { height: 6px; background: var(--bg3); border-radius: 6px; overflow: hidden; }
.bar > i { display: block; height: 100%; width: 0; background: linear-gradient(90deg,var(--accent),var(--accent2)); transition: width .4s; }
#overall .pct { font-size: 11px; color: var(--muted); margin-top: 4px; }

.mod { border-bottom: 1px solid var(--line); }
.mod > .mh {
  padding: 12px 20px; cursor: pointer;
  display: flex; align-items: center; gap: 8px;
  font-weight: 600; font-size: 13px; user-select: none;
}
.mod > .mh:hover { background: var(--bg3); }
.mod > .mh .chev { color: var(--muted); font-size: 10px; transition: transform .2s; margin-left: auto; }
.mod.open > .mh .chev { transform: rotate(90deg); }
.mod > .mh .midx { color: var(--accent2); font-family: var(--mono); font-size: 11px; }
.lessons { display: none; padding: 2px 0 8px; }
.mod.open .lessons { display: block; }
.lrow {
  padding: 7px 20px 7px 40px; cursor: pointer; font-size: 13px;
  color: var(--muted); display: flex; align-items: center; gap: 9px;
}
.lrow:hover { background: var(--bg3); color: var(--fg); }
.lrow.active { color: var(--fg); background: var(--bg3); box-shadow: inset 3px 0 0 var(--accent); }
.lrow .dot { width: 15px; height: 15px; border-radius: 50%; border: 1.5px solid var(--line); flex: 0 0 auto; display: grid; place-items: center; font-size: 9px; }
.lrow.done .dot { background: var(--accent); border-color: var(--accent); color: #04150d; }

/* ---------- main ---------- */
#main { overflow-y: auto; }
#content { max-width: 820px; margin: 0 auto; padding: 46px 40px 120px; }
.crumb { color: var(--muted); font-size: 12px; font-family: var(--mono); margin-bottom: 8px; }
h2.ltitle { font-size: 30px; margin: 0 0 22px; letter-spacing: -.6px; }
.read h3 { font-size: 18px; margin: 30px 0 10px; }
.read p { margin: 12px 0; }
.read ul, .read ol { margin: 12px 0; padding-left: 22px; }
.read li { margin: 5px 0; }
.read code { font-family: var(--mono); background: var(--bg3); padding: 2px 6px; border-radius: 5px; font-size: 13px; color: var(--accent); }
.read strong { color: #fff; }
.read a { color: var(--accent2); }
.note { border-left: 3px solid var(--accent2); background: var(--bg2); padding: 10px 16px; border-radius: 0 8px 8px 0; margin: 16px 0; }
.note.warn { border-color: var(--amber); }
.note b { color: #fff; }

pre.code {
  font-family: var(--mono); font-size: 13.5px; line-height: 1.55;
  background: #0a0e14; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 16px 18px; overflow-x: auto; margin: 16px 0;
}
pre.code .kw { color: #ff7b72; }
pre.code .ty { color: #79c0ff; }
pre.code .st { color: #a5d6ff; }
pre.code .nm { color: #f0b429; }
pre.code .cm { color: #6a7383; font-style: italic; }
pre.code .fn { color: #d2a8ff; }
pre.code .pp { color: #7ee787; }

/* ---------- exercises ---------- */
.ex {
  border: 1px solid var(--line); border-radius: var(--radius);
  background: var(--bg2); margin: 22px 0; overflow: hidden;
}
.ex .exhead { padding: 12px 18px; border-bottom: 1px solid var(--line); display: flex; align-items: center; gap: 10px; }
.ex .exhead .kind { font-size: 10px; text-transform: uppercase; letter-spacing: .8px; font-weight: 700; padding: 3px 8px; border-radius: 20px; }
.kind.mcq { background: rgba(88,166,255,.15); color: var(--accent2); }
.kind.predict { background: rgba(240,180,41,.15); color: var(--amber); }
.kind.code { background: rgba(78,227,154,.15); color: var(--accent); }
.ex .exhead .st { margin-left: auto; font-size: 18px; }
.ex .exbody { padding: 16px 18px; }
.ex .q { margin: 0 0 14px; }
.ex .q code { font-family: var(--mono); background: var(--bg3); padding: 1px 6px; border-radius: 5px; font-size: 13px; }

.opts { display: flex; flex-direction: column; gap: 8px; }
.opt {
  border: 1px solid var(--line); border-radius: 8px; padding: 10px 14px; cursor: pointer;
  font-family: var(--mono); font-size: 13px; background: var(--bg); transition: .12s;
}
.opt:hover { border-color: var(--accent2); }
.opt.sel { border-color: var(--accent2); background: rgba(88,166,255,.1); }
.opt.right { border-color: var(--accent); background: rgba(78,227,154,.12); }
.opt.wrong { border-color: var(--red); background: rgba(255,107,107,.12); }

textarea.ans {
  width: 100%; min-height: 44px; resize: vertical; font-family: var(--mono);
  font-size: 13.5px; line-height: 1.5; background: #0a0e14; color: var(--fg);
  border: 1px solid var(--line); border-radius: 8px; padding: 12px 14px;
}
textarea.ans.big { min-height: 120px; }
textarea.ans:focus { outline: none; border-color: var(--accent2); }
.exback { color: var(--muted); font-size: 12px; margin: 8px 0 0; font-family: var(--mono); }

.exfoot { display: flex; align-items: center; gap: 12px; margin-top: 14px; flex-wrap: wrap; }
button.btn {
  font-family: var(--sans); font-weight: 600; font-size: 13px; cursor: pointer;
  border: none; border-radius: 8px; padding: 9px 18px; background: var(--accent2); color: #06121f;
}
button.btn:hover { filter: brightness(1.1); }
button.btn.ghost { background: var(--bg3); color: var(--fg); }
button.btn:disabled { opacity: .5; cursor: default; }
.feedback { font-size: 13px; padding: 10px 14px; border-radius: 8px; margin-top: 12px; display: none; }
.feedback.show { display: block; }
.feedback.ok { background: rgba(78,227,154,.12); color: var(--accent); border: 1px solid rgba(78,227,154,.3); }
.feedback.no { background: rgba(255,107,107,.12); color: var(--red); border: 1px solid rgba(255,107,107,.3); }
.feedback b { color: #fff; }
.feedback pre { font-family: var(--mono); font-size: 12.5px; margin: 6px 0 0; white-space: pre-wrap; }

.lessonnav { display: flex; justify-content: space-between; margin-top: 46px; padding-top: 24px; border-top: 1px solid var(--line); }
.lessonnav button { font-family: var(--sans); font-size: 14px; font-weight: 600; cursor: pointer; border: 1px solid var(--line); background: var(--bg2); color: var(--fg); border-radius: 8px; padding: 11px 20px; }
.lessonnav button:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.lessonnav button:disabled { opacity: .35; cursor: default; }
.donebanner { margin-top: 22px; padding: 14px 18px; border-radius: var(--radius); background: rgba(78,227,154,.1); border: 1px solid rgba(78,227,154,.3); color: var(--accent); font-weight: 600; display: none; }
.donebanner.show { display: block; }

#welcome { text-align: center; padding: 80px 20px; }
#welcome h2 { font-size: 34px; margin: 0 0 10px; }
#welcome p { color: var(--muted); max-width: 520px; margin: 8px auto; }
#welcome .big { font-size: 60px; margin-bottom: 10px; }

@media (max-width: 820px) {
  body { grid-template-columns: 1fr; }
  #sidebar { position: fixed; z-index: 20; width: 300px; height: 100%; transform: translateX(-100%); transition: transform .25s; }
  body.nav-open #sidebar { transform: none; }
  #content { padding: 30px 20px 100px; }
  #menubtn { display: grid !important; }
}
/* ---------- accounts ---------- */
#authbox { margin-top: 14px; }
#authbtn {
  width: 100%; padding: 9px; cursor: pointer; font-family: var(--sans); font-weight: 600; font-size: 13px;
  background: var(--accent2); color: #06121f; border: none; border-radius: 8px;
}
#authbtn:hover { filter: brightness(1.08); }
#authbox .anon { font-size: 10.5px; color: var(--muted); margin-top: 5px; text-align: center; }
#authbox .who { display: flex; align-items: center; gap: 6px; font-size: 13px; }
#authbox .who .cloud { margin-left: auto; font-size: 10px; color: var(--accent); }
#authbox #logoutlink { font-size: 11px; color: var(--muted); }
#authbox #logoutlink:hover { color: var(--red); }

#authmodal {
  position: fixed; inset: 0; z-index: 50; background: rgba(0,0,0,.6);
  display: grid; place-items: center; padding: 20px; backdrop-filter: blur(3px);
}
.am-card {
  position: relative; width: 100%; max-width: 380px; background: var(--bg2);
  border: 1px solid var(--line); border-radius: 14px; padding: 26px 26px 20px;
}
.am-x { position: absolute; top: 12px; right: 14px; background: none; border: none; color: var(--muted); font-size: 16px; cursor: pointer; }
.am-x:hover { color: var(--fg); }
.am-tabs { display: flex; gap: 6px; margin-bottom: 18px; }
.am-tabs button {
  flex: 1; padding: 8px; cursor: pointer; font-family: var(--sans); font-weight: 600; font-size: 13px;
  background: var(--bg); color: var(--muted); border: 1px solid var(--line); border-radius: 8px;
}
.am-tabs button.on { background: var(--bg3); color: var(--fg); border-color: var(--accent2); }
.am-form { display: flex; flex-direction: column; }
.am-form label { font-size: 11px; color: var(--muted); font-weight: 600; margin: 10px 0 4px; }
.am-form input {
  font-family: var(--mono); font-size: 14px; background: var(--bg); color: var(--fg);
  border: 1px solid var(--line); border-radius: 8px; padding: 10px 12px;
}
.am-form input:focus { outline: none; border-color: var(--accent2); }
.am-hint { font-size: 10.5px; color: var(--muted); margin: 6px 0 2px; }
.am-err { color: var(--red); font-size: 12.5px; min-height: 16px; margin: 4px 0; }
.am-go { margin-top: 6px; }
.am-note { font-size: 11px; color: var(--muted); margin-top: 16px; line-height: 1.5; }
.am-or { display: flex; align-items: center; gap: 10px; margin: 16px 0 12px; color: var(--muted); font-size: 11px; }
.am-or::before, .am-or::after { content: ""; flex: 1; height: 1px; background: var(--line); }
.am-discord {
  display: flex; align-items: center; justify-content: center; gap: 9px;
  width: 100%; padding: 11px; border-radius: 8px; text-decoration: none;
  background: #5865F2; color: #fff; font-weight: 600; font-size: 14px;
}
.am-discord:hover { background: #4752c4; }

.toast {
  position: fixed; bottom: 24px; left: 50%; transform: translate(-50%, 20px);
  background: var(--bg3); color: var(--fg); border: 1px solid var(--line);
  padding: 12px 20px; border-radius: 10px; font-size: 13.5px; z-index: 60;
  opacity: 0; transition: opacity .25s, transform .25s; box-shadow: 0 8px 30px rgba(0,0,0,.5);
}
.toast.show { opacity: 1; transform: translate(-50%, 0); }

/* ---------- playground / run ---------- */
#pgbtn {
  width: 100%; margin-top: 12px; padding: 9px; cursor: pointer;
  font-family: var(--sans); font-weight: 600; font-size: 13px;
  background: rgba(78,227,154,.12); color: var(--accent);
  border: 1px solid rgba(78,227,154,.35); border-radius: 8px;
}
#pgbtn:hover { background: rgba(78,227,154,.2); }
.kind.run { background: rgba(120,110,255,.18); color: #a89bff; }
.kind.explain { background: rgba(240,180,41,.16); color: var(--amber); }
textarea.code-in { min-height: 160px; tab-size: 4; }
textarea.ans.prose { font-family: var(--sans); font-size: 14.5px; min-height: 90px; }
.pg-label { display: block; font-size: 12px; color: var(--muted); font-weight: 600; margin: 18px 0 6px; }
.spin { font-size: 12px; color: var(--amber); font-family: var(--mono); }
.ro {
  font-family: var(--mono); font-size: 13px; line-height: 1.5; white-space: pre-wrap; word-break: break-word;
  background: #0a0e14; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 14px 16px; margin-top: 12px; color: var(--fg); max-height: 360px; overflow: auto;
}
.ro-err { color: var(--red); }
.ro-dim { color: var(--muted); }

#menubtn { display: none; position: fixed; top: 14px; left: 14px; z-index: 30; width: 42px; height: 42px; border-radius: 8px; background: var(--bg3); border: 1px solid var(--line); color: var(--fg); place-items: center; cursor: pointer; font-size: 18px; }