/* ---------- Design tokens ---------- */
:root {
  --bg: #0d1117;
  --bg-soft: #121924;
  --panel: #161d2b;
  --panel-2: #1c2536;
  --border: #263149;
  --text: #e6edf6;
  --muted: #93a3ba;
  --accent: #4f9dff;
  --accent-2: #7c5cff;
  --ok: #3fb950;
  --warn: #d29922;
  --bad: #f85149;
  --radius: 14px;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --sans: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
}
:root[data-theme="light"] {
  --bg: #f5f7fb;
  --bg-soft: #eef2f9;
  --panel: #ffffff;
  --panel-2: #f2f5fb;
  --border: #d9e0ec;
  --text: #101726;
  --muted: #5a6b85;
  --accent: #1f6feb;
  --accent-2: #6b46ff;
  --ok: #1a7f37;
  --warn: #9a6700;
  --bad: #cf222e;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

#app { display: flex; min-height: 100vh; }

/* ---------- Sidebar ---------- */
.sidebar {
  width: 264px;
  flex: 0 0 264px;
  background: var(--bg-soft);
  border-right: 1px solid var(--border);
  padding: 18px 14px;
  display: flex;
  flex-direction: column;
  gap: 18px;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
}
.brand { display: flex; gap: 10px; align-items: center; }
.brand small { display: block; color: var(--muted); font-size: 12px; line-height: 1.2; }
.brand-mark {
  width: 38px; height: 38px; border-radius: 11px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #fff; font-weight: 800; display: grid; place-items: center;
}
#nav { display: flex; flex-direction: column; gap: 2px; }
#nav a {
  color: var(--muted); text-decoration: none; padding: 9px 11px;
  border-radius: 10px; font-size: 14px; display: flex; align-items: center; gap: 8px;
}
#nav a:hover { background: var(--panel); color: var(--text); }
#nav a.active { background: var(--panel-2); color: var(--text); box-shadow: inset 2px 0 0 var(--accent); }
.sidebar-foot { margin-top: auto; display: flex; flex-direction: column; gap: 10px; }
.xp-box { background: var(--panel); border: 1px solid var(--border); border-radius: 12px; padding: 10px 12px; }
.xp-row { display: flex; justify-content: space-between; font-size: 13px; color: var(--muted); }
.xp-row strong { color: var(--text); }

/* ---------- Layout ---------- */
.view { flex: 1; padding: 26px 32px 90px; max-width: 1180px; }
h1 { font-size: 26px; margin: 0 0 6px; letter-spacing: -0.02em; }
h2 { font-size: 20px; margin: 26px 0 10px; letter-spacing: -0.01em; }
h3 { font-size: 16px; margin: 20px 0 8px; }
p { margin: 10px 0; }
a { color: var(--accent); }
.sub { color: var(--muted); margin: 0 0 18px; }
.grid { display: grid; gap: 14px; }
.grid.c2 { grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); }
.grid.c3 { grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); }
.grid.c4 { grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); }
.row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.spacer { flex: 1; }
.hidden { display: none !important; }

/* ---------- Card ---------- */
.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 18px;
}
.card.tight { padding: 12px 14px; }
.card h3:first-child, .card h2:first-child { margin-top: 0; }
.card-link { text-decoration: none; color: inherit; display: block; transition: transform .12s ease, border-color .12s ease; }
.card-link:hover { transform: translateY(-2px); border-color: var(--accent); }

.stat { text-align: left; }
.stat .n { font-size: 28px; font-weight: 750; letter-spacing: -0.02em; }
.stat .l { color: var(--muted); font-size: 13px; }

/* ---------- Buttons & badges ---------- */
.btn {
  background: var(--accent); color: #fff; border: 0; border-radius: 10px;
  padding: 9px 15px; font-size: 14px; font-weight: 600; cursor: pointer;
  font-family: inherit;
}
.btn:hover { filter: brightness(1.08); }
.btn:disabled { opacity: .5; cursor: not-allowed; }
.btn.ghost { background: transparent; border: 1px solid var(--border); color: var(--text); }
.btn.ghost:hover { border-color: var(--accent); }
.btn.small { padding: 6px 11px; font-size: 13px; }
.btn.warn { background: var(--warn); color: #12161f; }
.btn.danger { background: transparent; border: 1px solid var(--bad); color: var(--bad); }

.badge {
  display: inline-block; padding: 2px 8px; border-radius: 999px;
  font-size: 11.5px; font-weight: 700; background: var(--panel-2); color: var(--muted);
  border: 1px solid var(--border);
}
.badge.easy { color: var(--ok); border-color: color-mix(in srgb, var(--ok) 45%, transparent); }
.badge.medium { color: var(--warn); border-color: color-mix(in srgb, var(--warn) 45%, transparent); }
.badge.hard { color: var(--bad); border-color: color-mix(in srgb, var(--bad) 45%, transparent); }
.badge.ok { color: var(--ok); border-color: color-mix(in srgb, var(--ok) 45%, transparent); }
.badge.accent { color: var(--accent); border-color: color-mix(in srgb, var(--accent) 45%, transparent); }

/* ---------- Progress ---------- */
.bar { height: 8px; background: var(--panel-2); border-radius: 999px; overflow: hidden; border: 1px solid var(--border); }
.bar > i { display: block; height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent-2)); }
.bar.slim { height: 6px; }

/* ---------- Markdown content ---------- */
.md { font-size: 15px; }
.md h2 { border-bottom: 1px solid var(--border); padding-bottom: 6px; }
.md ul, .md ol { padding-left: 22px; margin: 10px 0; }
.md li { margin: 5px 0; }
.md code { font-family: var(--mono); font-size: 13px; background: var(--panel-2); padding: 2px 6px; border-radius: 6px; border: 1px solid var(--border); }
.md pre { background: var(--panel-2); border: 1px solid var(--border); border-radius: 12px; padding: 13px 15px; overflow-x: auto; }
.md pre code { background: none; border: 0; padding: 0; font-size: 13px; line-height: 1.6; }
.md blockquote {
  margin: 12px 0; padding: 8px 14px; border-left: 3px solid var(--accent);
  background: var(--panel-2); border-radius: 0 10px 10px 0; color: var(--text);
}
.md table { border-collapse: collapse; width: 100%; margin: 12px 0; font-size: 14px; display: block; overflow-x: auto; }
.md th, .md td { border: 1px solid var(--border); padding: 7px 10px; text-align: left; }
.md th { background: var(--panel-2); }
.md hr { border: 0; border-top: 1px solid var(--border); margin: 20px 0; }

/* ---------- Problem workspace ---------- */
.workspace { display: grid; grid-template-columns: minmax(340px, 1fr) minmax(420px, 1.15fr); gap: 16px; align-items: start; }
@media (max-width: 1080px) { .workspace { grid-template-columns: 1fr; } }
.pane { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); }
.pane-head {
  display: flex; align-items: center; gap: 10px; padding: 10px 14px;
  border-bottom: 1px solid var(--border);
}
.pane-body { padding: 14px 16px; }
.pane-body.scroll { max-height: 62vh; overflow-y: auto; }

.editor-wrap { position: relative; }
textarea.editor {
  width: 100%; min-height: 340px; resize: vertical;
  background: var(--bg); color: var(--text);
  border: 0; border-radius: 0 0 var(--radius) var(--radius);
  padding: 14px 16px; font-family: var(--mono); font-size: 13.5px; line-height: 1.6;
  tab-size: 2; outline: none;
}
textarea.editor:focus { box-shadow: inset 0 0 0 1px var(--accent); }

.tests { display: flex; flex-direction: column; gap: 8px; }
.test {
  border: 1px solid var(--border); border-radius: 10px; padding: 8px 12px;
  background: var(--panel-2); font-size: 13px;
}
.test.pass { border-color: color-mix(in srgb, var(--ok) 50%, transparent); }
.test.fail { border-color: color-mix(in srgb, var(--bad) 55%, transparent); }
.test .k { color: var(--muted); font-size: 12px; }
.test pre { margin: 4px 0 0; font-family: var(--mono); font-size: 12.5px; white-space: pre-wrap; word-break: break-word; }

.hint {
  border: 1px solid var(--border); border-left: 3px solid var(--accent-2);
  border-radius: 0 10px 10px 0; padding: 10px 13px; background: var(--panel-2); margin: 8px 0;
}
.diag { border-left-color: var(--warn); }

.kbd {
  font-family: var(--mono); font-size: 11.5px; border: 1px solid var(--border);
  border-bottom-width: 2px; border-radius: 6px; padding: 1px 6px; background: var(--panel-2);
}

/* ---------- Quiz ---------- */
.quiz-q { border: 1px solid var(--border); border-radius: 12px; padding: 14px 16px; background: var(--panel); margin: 12px 0; }
.opt { display: flex; gap: 10px; align-items: flex-start; padding: 9px 12px; border: 1px solid var(--border);
  border-radius: 10px; margin: 6px 0; cursor: pointer; background: var(--panel-2); }
.opt:hover { border-color: var(--accent); }
.opt.selected { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); }
.opt.correct { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 12%, var(--panel-2)); }
.opt.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 12%, var(--panel-2)); }
.opt input { margin-top: 4px; }

/* ---------- Table list ---------- */
.list { display: flex; flex-direction: column; gap: 6px; }
.list-item {
  display: flex; align-items: center; gap: 10px; padding: 10px 13px;
  border: 1px solid var(--border); border-radius: 11px; background: var(--panel);
  text-decoration: none; color: inherit;
}
.list-item:hover { border-color: var(--accent); }
.list-item .t { font-weight: 600; }
.list-item .m { color: var(--muted); font-size: 12.5px; }

/* ---------- Day timeline ---------- */
.day {
  border: 1px solid var(--border); border-radius: 12px; background: var(--panel);
  padding: 13px 15px; display: flex; gap: 14px; align-items: flex-start;
}
.day .num {
  width: 42px; height: 42px; flex: 0 0 42px; border-radius: 12px; display: grid; place-items: center;
  background: var(--panel-2); border: 1px solid var(--border); font-weight: 750;
}
.day.done .num { background: color-mix(in srgb, var(--ok) 22%, var(--panel-2)); border-color: var(--ok); color: var(--ok); }
.day.today { border-color: var(--accent); box-shadow: 0 0 0 1px var(--accent); }

/* ---------- Toast ---------- */
.toast {
  position: fixed; bottom: 22px; left: 50%; transform: translateX(-50%);
  background: var(--panel); border: 1px solid var(--accent); color: var(--text);
  padding: 11px 18px; border-radius: 12px; z-index: 50; font-size: 14px;
  box-shadow: 0 12px 30px rgba(0,0,0,.35);
}

/* ---------- Misc ---------- */
.muted { color: var(--muted); }
.small { font-size: 13px; }
.mono { font-family: var(--mono); }
.pill-row { display: flex; gap: 6px; flex-wrap: wrap; }
.center { text-align: center; }
details.spoiler { border: 1px solid var(--border); border-radius: 12px; padding: 10px 14px; background: var(--panel-2); margin: 10px 0; }
details.spoiler > summary { cursor: pointer; font-weight: 650; }

@media (max-width: 820px) {
  #app { flex-direction: column; }
  .sidebar { width: 100%; flex: none; height: auto; position: static; }
  #nav { flex-direction: row; flex-wrap: wrap; }
  .view { padding: 18px 16px 70px; }
}