/* SE Practice Bench — dark navy / steel grey / amber */
:root {
  --bg: #0c141f;
  --bg-accent: #0f1a29;
  --panel: #142132;
  --panel-2: #1a2a40;
  --line: #263a54;
  --line-soft: #1e3049;
  --text: #e9eef5;
  --muted: #8fa3b8;
  --steel: #aebfd1;
  --amber: #f5a623;
  --amber-soft: #ffc65c;
  --good: #52b788;
  --bad: #e26d5c;
  --radius: 10px;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background:
    radial-gradient(1200px 500px at 80% -10%, rgba(245, 166, 35, 0.06), transparent 60%),
    radial-gradient(900px 500px at 10% -20%, rgba(70, 110, 160, 0.12), transparent 60%),
    var(--bg);
  color: var(--text);
  font: 16px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ---------- top bar ---------- */
.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 10px 22px;
  background: rgba(12, 20, 31, 0.92);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--line-soft);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text);
}

.brand-mark {
  font-size: 30px;
  line-height: 1;
  color: var(--amber);
  transform: translateY(-1px);
}

.brand-text {
  font-weight: 700;
  font-size: 18px;
  letter-spacing: 0.2px;
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.brand-text small {
  font-weight: 500;
  font-size: 11.5px;
  color: var(--muted);
  letter-spacing: 0.8px;
  text-transform: uppercase;
}

.topbar-stats {
  font-size: 13px;
  color: var(--muted);
  font-family: var(--mono);
  white-space: nowrap;
}
.topbar-stats b { color: var(--amber); font-weight: 600; }

/* ---------- layout ---------- */
main {
  flex: 1;
  width: 100%;
  max-width: 980px;
  margin: 0 auto;
  padding: 28px 20px 60px;
}

.footer {
  border-top: 1px solid var(--line-soft);
  padding: 18px 22px 26px;
  color: var(--muted);
  font-size: 12.5px;
  max-width: 980px;
  margin: 0 auto;
}

/* ---------- home ---------- */
.hero { margin: 8px 0 26px; }
.hero h1 {
  margin: 0 0 8px;
  font-size: 30px;
  letter-spacing: -0.3px;
}
.hero h1 span { color: var(--amber); }
.hero p { margin: 0; color: var(--steel); max-width: 640px; }

.component-block { margin-bottom: 34px; }

.component-head {
  display: flex;
  align-items: baseline;
  gap: 12px;
  border-bottom: 1px solid var(--line-soft);
  padding-bottom: 8px;
  margin-bottom: 16px;
}
.component-head h2 { margin: 0; font-size: 20px; }
.component-head .tag {
  font-size: 11px;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: var(--amber);
  border: 1px solid rgba(245, 166, 35, 0.4);
  border-radius: 99px;
  padding: 2px 10px;
}

.section-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(290px, 1fr));
  gap: 14px;
}

.section-card {
  display: block;
  text-decoration: none;
  color: inherit;
  background: linear-gradient(160deg, var(--panel-2), var(--panel));
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 16px 14px;
  transition: border-color 0.15s ease, transform 0.15s ease;
}
.section-card:hover {
  border-color: var(--amber);
  transform: translateY(-2px);
}
.section-card h3 { margin: 0 0 4px; font-size: 16.5px; }
.section-card .sub {
  color: var(--muted);
  font-size: 12.5px;
  margin: 0 0 14px;
  line-height: 1.45;
}

.progress-row {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--muted);
  font-family: var(--mono);
  margin-bottom: 6px;
}
.progress-row .ok { color: var(--good); }

.bar {
  height: 6px;
  border-radius: 4px;
  background: #0a121d;
  border: 1px solid var(--line-soft);
  overflow: hidden;
  position: relative;
}
.bar i {
  position: absolute;
  left: 0; top: 0; bottom: 0;
  background: var(--steel);
  opacity: 0.55;
}
.bar b {
  position: absolute;
  left: 0; top: 0; bottom: 0;
  background: linear-gradient(90deg, var(--amber), var(--amber-soft));
}

.home-actions { margin-top: 6px; text-align: right; }

/* ---------- buttons & links ---------- */
.btn {
  display: inline-block;
  border: 1px solid var(--line);
  background: var(--panel-2);
  color: var(--text);
  border-radius: 8px;
  padding: 8px 16px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  transition: border-color 0.12s ease, background 0.12s ease;
}
.btn:hover { border-color: var(--amber); }
.btn.primary {
  background: var(--amber);
  border-color: var(--amber);
  color: #1a1205;
}
.btn.primary:hover { background: var(--amber-soft); border-color: var(--amber-soft); }
.btn.ghost {
  background: transparent;
  color: var(--muted);
  font-weight: 500;
}
.btn.ghost:hover { color: var(--bad); border-color: var(--bad); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }

.backlink {
  display: inline-block;
  color: var(--muted);
  text-decoration: none;
  font-size: 13.5px;
  margin-bottom: 14px;
}
.backlink:hover { color: var(--amber); }

/* ---------- section view ---------- */
.section-head { margin-bottom: 22px; }
.section-head h1 { margin: 0 0 4px; font-size: 24px; }
.section-head .sub { color: var(--steel); font-size: 14px; margin: 0 0 14px; }
.section-head .bar { max-width: 420px; }
.section-toolbar {
  display: flex;
  gap: 10px;
  align-items: center;
  margin-top: 14px;
  flex-wrap: wrap;
}

.domain-group { margin-bottom: 22px; }
.domain-group h2 {
  font-size: 12px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: var(--muted);
  margin: 0 0 8px;
  border-bottom: 1px dashed var(--line-soft);
  padding-bottom: 6px;
}

.problem-row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 12px;
  border: 1px solid transparent;
  border-radius: 8px;
  text-decoration: none;
  color: inherit;
}
.problem-row:hover { background: var(--panel); border-color: var(--line); }
.problem-row .num {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--muted);
  width: 30px;
  flex: none;
}
.problem-row .t { flex: 1; font-size: 15px; }
.problem-row .kind {
  font-size: 10.5px;
  letter-spacing: 0.8px;
  text-transform: uppercase;
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 99px;
  padding: 1px 8px;
  flex: none;
}
.dot {
  width: 10px; height: 10px;
  border-radius: 50%;
  border: 1.5px solid var(--muted);
  flex: none;
}
.dot.correct { background: var(--good); border-color: var(--good); }
.dot.incorrect { background: var(--bad); border-color: var(--bad); }

/* ---------- problem view ---------- */
.crumbs {
  font-size: 13px;
  color: var(--muted);
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}
.crumbs a { color: var(--muted); text-decoration: none; }
.crumbs a:hover { color: var(--amber); }

.problem-card {
  background: linear-gradient(170deg, var(--panel-2), var(--panel));
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 24px 26px;
}

.problem-meta {
  display: flex;
  gap: 10px;
  align-items: center;
  flex-wrap: wrap;
  margin-bottom: 14px;
}
.problem-meta .domain {
  font-size: 11px;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: var(--amber);
  border: 1px solid rgba(245, 166, 35, 0.4);
  border-radius: 99px;
  padding: 2px 10px;
}
.problem-meta .ref {
  font-size: 12px;
  color: var(--muted);
  font-family: var(--mono);
}
.problem-meta .prev-state { font-size: 12px; color: var(--muted); margin-left: auto; }
.problem-meta .prev-state.ok { color: var(--good); }
.problem-meta .prev-state.no { color: var(--bad); }

.problem-card h1 { font-size: 21px; margin: 0 0 14px; }

.question { font-size: 15.5px; color: var(--text); }
.question p { margin: 10px 0; }

/* diagrams (SVG figures embedded in questions & solutions) */
.diagram {
  margin: 16px 0;
  background: #0a121d;
  border: 1px solid var(--line-soft);
  border-radius: 8px;
  padding: 12px;
  text-align: center;
}
.diagram svg {
  width: 100%;
  max-width: 420px;
  height: auto;
}

/* completion banner + generated-set note (section view) */
.complete-banner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
  background: linear-gradient(160deg, rgba(82, 183, 136, 0.14), var(--panel));
  border: 1px solid var(--good);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 20px;
}
.complete-banner span { display: block; color: var(--steel); font-size: 13px; margin-top: 3px; }
.gen-note {
  background: rgba(245, 166, 35, 0.1);
  border: 1px solid rgba(245, 166, 35, 0.4);
  color: var(--amber-soft);
  border-radius: 8px;
  padding: 10px 14px;
  font-size: 13.5px;
  margin-bottom: 20px;
}
.gen-note strong { color: var(--amber); }

.eq {
  font-family: var(--mono);
  font-size: 14px;
  background: #0a121d;
  border-left: 3px solid var(--amber);
  border-radius: 4px;
  padding: 8px 14px;
  margin: 10px 0;
  overflow-x: auto;
}

/* options */
.options { margin: 20px 0 6px; display: grid; gap: 9px; }
.opt {
  display: flex;
  align-items: baseline;
  gap: 12px;
  text-align: left;
  width: 100%;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 11px 14px;
  color: var(--text);
  font: inherit;
  font-size: 15px;
  cursor: pointer;
  transition: border-color 0.12s ease;
}
.opt:hover { border-color: var(--steel); }
.opt .letter {
  font-family: var(--mono);
  font-weight: 700;
  font-size: 13px;
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 1px 7px;
  flex: none;
}
.opt.selected { border-color: var(--amber); background: rgba(245, 166, 35, 0.08); }
.opt.selected .letter { color: var(--amber); border-color: var(--amber); }
.opt.reveal-correct { border-color: var(--good); background: rgba(82, 183, 136, 0.1); }
.opt.reveal-correct .letter { color: var(--good); border-color: var(--good); }
.opt.reveal-wrong { border-color: var(--bad); background: rgba(226, 109, 92, 0.1); }
.opt.reveal-wrong .letter { color: var(--bad); border-color: var(--bad); }
.opt:disabled { cursor: default; }

/* numeric answer */
.num-answer {
  display: flex;
  gap: 10px;
  align-items: center;
  margin: 20px 0 6px;
  flex-wrap: wrap;
}
.num-answer input {
  background: #0a121d;
  border: 1px solid var(--line);
  color: var(--text);
  font-family: var(--mono);
  font-size: 16px;
  border-radius: 8px;
  padding: 10px 14px;
  width: 200px;
}
.num-answer input:focus { outline: none; border-color: var(--amber); }
.num-answer .unit { color: var(--muted); font-family: var(--mono); font-size: 14px; }

.answer-actions {
  display: flex;
  gap: 10px;
  margin-top: 18px;
  align-items: center;
  flex-wrap: wrap;
}

/* result + solution */
.result-banner {
  margin-top: 20px;
  border-radius: 8px;
  padding: 12px 16px;
  font-weight: 700;
  font-size: 15px;
}
.result-banner.ok {
  background: rgba(82, 183, 136, 0.12);
  border: 1px solid var(--good);
  color: var(--good);
}
.result-banner.no {
  background: rgba(226, 109, 92, 0.12);
  border: 1px solid var(--bad);
  color: var(--bad);
}
.result-banner small { display: block; font-weight: 500; color: var(--steel); margin-top: 2px; }

.solution {
  margin-top: 18px;
  border-top: 1px dashed var(--line);
  padding-top: 16px;
}
.solution h2 {
  font-size: 12px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
  color: var(--amber);
  margin: 0 0 10px;
}
.solution p, .solution li { font-size: 15px; color: var(--text); }
.solution .ref-line {
  margin-top: 14px;
  font-size: 12.5px;
  color: var(--muted);
  font-family: var(--mono);
}

.pager {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  margin-top: 18px;
}

sub, sup { line-height: 0; }

@media (max-width: 560px) {
  .topbar-stats { display: none; }
  .problem-card { padding: 18px 16px; }
}