:root {
  --bg: #0f1419;
  --bg-elev: #171e27;
  --bg-card: #1c2530;
  --bg-card-hover: #222d3a;
  --border: #2a3744;
  --text: #e8edf2;
  --text-dim: #9fb0c0;
  --text-faint: #6b7d8f;
  --accent: #4f9dff;
  --accent-2: #7c5cff;
  --good: #36c98a;
  --warn: #f2b441;
  --bad: #ff6b6b;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 6px 24px rgba(0,0,0,0.35);
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.5;
}
body { overflow-x: hidden; }

/* Wide display-mode equations scroll inside their own container instead of
   stretching the page on narrow screens. */
mjx-container { max-width: 100%; }
mjx-container[display="true"] {
  display: block;
  overflow-x: auto;
  overflow-y: hidden;
  padding-bottom: 4px;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- Top bar ---------- */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.7rem 1.5rem;
  background: var(--bg-elev);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 50;
}
.brand { display: flex; align-items: baseline; gap: 0.5rem; cursor: pointer; }
.brand-mark { color: var(--accent); font-size: 1.3rem; }
.brand-name { font-weight: 700; font-size: 1.25rem; letter-spacing: -0.01em; }
.brand-sub { color: var(--text-faint); font-size: 0.82rem; }
.topnav { display: flex; gap: 1.2rem; }
.topnav a { color: var(--text-dim); font-weight: 500; font-size: 0.95rem; }
.topnav a:hover, .topnav a.active { color: var(--text); text-decoration: none; }

.app { max-width: 1100px; margin: 0 auto; padding: 1.8rem 1.5rem 3rem; min-height: 70vh; }

/* ---------- Footer ---------- */
.footer {
  border-top: 1px solid var(--border);
  padding: 1rem 1.5rem;
  color: var(--text-faint);
  font-size: 0.8rem;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  max-width: 1100px;
  margin: 0 auto;
}
.footer-disclaimer { font-size: 0.74rem; }

/* ---------- Generic ---------- */
.page-title { font-size: 1.7rem; margin: 0 0 0.3rem; letter-spacing: -0.02em; }
.page-sub { color: var(--text-dim); margin: 0 0 1.6rem; }
.section-title { font-size: 1.15rem; margin: 1.8rem 0 0.8rem; }
.muted { color: var(--text-dim); }
.faint { color: var(--text-faint); }
.pill {
  display: inline-block; padding: 0.15rem 0.6rem; border-radius: 999px;
  font-size: 0.72rem; font-weight: 600; background: var(--bg-card); border: 1px solid var(--border);
  color: var(--text-dim);
}
.pill.accent { background: rgba(79,157,255,0.12); border-color: rgba(79,157,255,0.4); color: var(--accent); }

.btn {
  display: inline-flex; align-items: center; gap: 0.4rem;
  background: var(--accent); color: #fff; border: none;
  padding: 0.6rem 1.1rem; border-radius: var(--radius-sm);
  font-size: 0.95rem; font-weight: 600; cursor: pointer; font-family: var(--font);
  transition: filter 0.15s, transform 0.05s;
}
.btn:hover { filter: brightness(1.08); }
.btn:active { transform: translateY(1px); }
.btn.secondary { background: var(--bg-card); color: var(--text); border: 1px solid var(--border); }
.btn.secondary:hover { background: var(--bg-card-hover); }
.btn.ghost { background: transparent; color: var(--text-dim); border: 1px solid var(--border); }
.btn.small { padding: 0.4rem 0.8rem; font-size: 0.85rem; }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn-row { display: flex; gap: 0.7rem; flex-wrap: wrap; align-items: center; }

/* ---------- Cards / grids ---------- */
.grid { display: grid; gap: 1rem; }
.grid.cols-2 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.grid.cols-3 { grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); }

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.2rem;
}
.card.clickable { cursor: pointer; transition: background 0.15s, border-color 0.15s, transform 0.08s; }
.card.clickable:hover { background: var(--bg-card-hover); border-color: var(--accent); transform: translateY(-2px); }

/* ---------- Exam cards ---------- */
.exam-card { display: flex; flex-direction: column; gap: 0.6rem; }
.exam-card .ec-head { display: flex; align-items: center; justify-content: space-between; }
.exam-card .ec-name { font-size: 1.25rem; font-weight: 700; }
.exam-card .ec-full { color: var(--text-dim); font-size: 0.85rem; }
.exam-card .ec-meta { color: var(--text-faint); font-size: 0.8rem; }
.exam-badge {
  width: 42px; height: 42px; border-radius: 10px; display: flex; align-items: center;
  justify-content: center; font-weight: 800; font-size: 0.95rem; color: #fff;
}

/* ---------- Progress bars ---------- */
.bar { height: 8px; background: var(--bg); border-radius: 999px; overflow: hidden; }
.bar > span { display: block; height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent-2)); border-radius: 999px; transition: width 0.4s; }
.bar.good > span { background: linear-gradient(90deg, var(--good), #2ea3c9); }
.bar.warn > span { background: linear-gradient(90deg, var(--warn), #f28a41); }
.bar-label { display: flex; justify-content: space-between; font-size: 0.8rem; color: var(--text-dim); margin-bottom: 0.3rem; }

/* ---------- Stats ---------- */
.stat-row { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 1rem; }
.stat { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius); padding: 1rem 1.2rem; }
.stat .num { font-size: 1.9rem; font-weight: 700; letter-spacing: -0.02em; }
.stat .lbl { color: var(--text-dim); font-size: 0.82rem; }
.stat .num.good { color: var(--good); }
.stat .num.warn { color: var(--warn); }

/* ---------- Topic list ---------- */
.topic-row { display: flex; align-items: center; gap: 1rem; padding: 0.55rem 0; border-bottom: 1px solid var(--border); }
.topic-row:last-child { border-bottom: none; }
.topic-name { flex: 0 0 40%; font-size: 0.92rem; }
.topic-bar { flex: 1; }
.topic-stat { flex: 0 0 70px; text-align: right; font-size: 0.82rem; color: var(--text-dim); }

/* ---------- Papers catalogue ---------- */
.paper-row {
  display: flex; align-items: center; justify-content: space-between; gap: 1rem;
  padding: 0.7rem 0.9rem; border: 1px solid var(--border); border-radius: var(--radius-sm);
  margin-bottom: 0.5rem; background: var(--bg-card);
}
.paper-row .pr-info { display: flex; flex-direction: column; }
.paper-row .pr-name { font-weight: 600; }
.paper-row .pr-meta { color: var(--text-faint); font-size: 0.8rem; }

/* ---------- Question view ---------- */
.q-wrap { max-width: 820px; margin: 0 auto; }
.q-toolbar { display: flex; align-items: center; justify-content: space-between; margin-bottom: 1rem; flex-wrap: wrap; gap: 0.6rem; }
.q-card { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius); padding: 1.5rem; }
.q-stem { font-size: 1.05rem; line-height: 1.7; }
.q-stem p { margin: 0.6rem 0; }
.q-source { margin-top: 0.8rem; font-size: 0.78rem; color: var(--text-faint); }

.opt-list { list-style: none; padding: 0; margin: 1.2rem 0 0; display: flex; flex-direction: column; gap: 0.55rem; }
.opt {
  display: flex; gap: 0.7rem; align-items: flex-start; padding: 0.7rem 0.9rem;
  border: 1px solid var(--border); border-radius: var(--radius-sm); cursor: pointer;
  background: var(--bg-elev); transition: border-color 0.12s, background 0.12s;
}
.opt:hover { border-color: var(--accent); }
.opt.selected { border-color: var(--accent); background: rgba(79,157,255,0.10); }
.opt.correct { border-color: var(--good); background: rgba(54,201,138,0.12); }
.opt.incorrect { border-color: var(--bad); background: rgba(255,107,107,0.12); }
.opt .opt-key { font-weight: 700; color: var(--text-dim); flex: 0 0 1.2rem; }

.hint-box { margin-top: 1rem; background: var(--bg-elev); border: 1px dashed var(--border); border-radius: var(--radius-sm); padding: 1rem; }
.hint-box h4 { margin: 0 0 0.5rem; font-size: 0.9rem; color: var(--warn); }
.hint-item { padding: 0.5rem 0; border-bottom: 1px solid var(--border); }
.hint-item:last-child { border-bottom: none; }
.hint-item .hint-n { color: var(--warn); font-weight: 700; margin-right: 0.4rem; }

.solution-box { margin-top: 1rem; background: rgba(54,201,138,0.06); border: 1px solid rgba(54,201,138,0.3); border-radius: var(--radius-sm); padding: 1.2rem; }
.solution-box h4 { margin: 0 0 0.6rem; color: var(--good); font-size: 0.95rem; }
.solution-box .sol-body { line-height: 1.7; }
.solution-box .sol-body p { margin: 0.5rem 0; }

.self-mark { margin-top: 1rem; display: flex; gap: 0.7rem; align-items: center; flex-wrap: wrap; }

.difficulty { display: inline-flex; gap: 2px; }
.difficulty .dot { width: 7px; height: 7px; border-radius: 50%; background: var(--border); }
.difficulty .dot.on { background: var(--warn); }

/* ---------- Mock exam ---------- */
.timer { font-variant-numeric: tabular-nums; font-size: 1.3rem; font-weight: 700; padding: 0.3rem 0.8rem; border-radius: var(--radius-sm); background: var(--bg-card); border: 1px solid var(--border); }
.timer.low { color: var(--bad); border-color: var(--bad); }
.qnav { display: flex; flex-wrap: wrap; gap: 0.4rem; margin: 1rem 0; }
.qnav button {
  width: 36px; height: 36px; border-radius: 8px; border: 1px solid var(--border);
  background: var(--bg-card); color: var(--text-dim); cursor: pointer; font-weight: 600;
}
.qnav button.answered { border-color: var(--accent); color: var(--accent); }
.qnav button.current { background: var(--accent); color: #fff; border-color: var(--accent); }
.qnav button.flagged { box-shadow: inset 0 0 0 2px var(--warn); }

/* ---------- Charts (inline SVG) ---------- */
.chart { width: 100%; }
.chart text { fill: var(--text-faint); font-size: 11px; }
.chart .axis { stroke: var(--border); }
.chart .barfill { fill: var(--accent); }
.chart .line { fill: none; stroke: var(--accent); stroke-width: 2; }
.chart .dot { fill: var(--accent); }

/* ---------- Misc ---------- */
.back-link { color: var(--text-dim); font-size: 0.9rem; display: inline-flex; align-items: center; gap: 0.3rem; margin-bottom: 1rem; }
.empty { text-align: center; color: var(--text-faint); padding: 2.5rem 1rem; }
.filter-bar { display: flex; gap: 0.6rem; flex-wrap: wrap; align-items: center; margin-bottom: 1.2rem; }
select, input[type="text"] {
  background: var(--bg-card); border: 1px solid var(--border); color: var(--text);
  border-radius: var(--radius-sm); padding: 0.45rem 0.6rem; font-family: var(--font); font-size: 0.9rem;
}
.banner { background: rgba(242,180,65,0.1); border: 1px solid rgba(242,180,65,0.4); border-radius: var(--radius-sm); padding: 0.8rem 1rem; font-size: 0.88rem; color: var(--text); margin-bottom: 1.2rem; }
.banner.info { background: rgba(79,157,255,0.08); border-color: rgba(79,157,255,0.35); }

.feedback { margin-top: 1rem; padding: 0.8rem 1rem; border-radius: var(--radius-sm); font-weight: 600; }
.feedback.ok { background: rgba(54,201,138,0.12); color: var(--good); border: 1px solid rgba(54,201,138,0.4); }
.feedback.no { background: rgba(255,107,107,0.12); color: var(--bad); border: 1px solid rgba(255,107,107,0.4); }

@media (max-width: 640px) {
  .brand-sub { display: none; }
  .topnav { gap: 0.8rem; }
  .topic-name { flex-basis: 35%; }
}