:root {
  --bc-green-950: #17382c;
  --bc-green-900: #214d3d;
  --bc-green-800: #35624f;
  --bc-green-100: #dce8e1;
  --bc-green-50: #edf1ed;
  --bc-ink: #1d2420;
  --bc-copy: #3f4943;
  --bc-muted: #69716c;
  --bc-line: #d9ded9;
  --bc-line-dark: #bcc8c0;
  --bc-paper: #fffdfa;
  --bc-canvas: #f6f4ee;
  --bc-red: #9b433a;
  --bc-red-soft: #f9eeeb;
  --bc-amber: #916a31;
  --bc-amber-soft: #fff9ed;
  --bc-blue: #486a78;
  --bc-blue-soft: #edf1f3;
  --bc-shadow: 0 1px 2px rgba(29, 36, 32, 0.045), 0 8px 22px rgba(29, 36, 32, 0.035);
  --bc-radius: 10px;
  --bc-serif: Georgia, "Times New Roman", "Noto Serif SC", serif;
  --bc-sans: Inter, "Source Sans 3", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --bc-mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
}

* { box-sizing: border-box; }

html { color-scheme: light; scroll-behavior: smooth; }

body.bc-learning-page {
  margin: 0;
  min-width: 320px;
  color: var(--bc-copy);
  background: var(--bc-canvas);
  font-family: var(--bc-sans);
  font-size: 15px;
  line-height: 1.55;
}

button, input, select, textarea { font: inherit; }
a { color: inherit; }
button { color: inherit; }
[hidden] { display: none !important; }

.bc-skip {
  position: fixed;
  z-index: 100;
  top: 8px;
  left: 8px;
  padding: 9px 14px;
  color: #fff;
  background: var(--bc-green-950);
  border-radius: 5px;
  transform: translateY(-150%);
}
.bc-skip:focus { transform: none; }

.bc-topbar {
  position: sticky;
  z-index: 30;
  top: 0;
  display: grid;
  grid-template-columns: 165px minmax(0, 1fr) auto;
  min-height: 68px;
  background: var(--bc-paper);
  border-bottom: 1px solid var(--bc-line);
  backdrop-filter: none;
}

.bc-brand {
  display: flex;
  align-items: center;
  justify-content: flex-start;
  padding: 9px 16px;
  color: var(--bc-ink);
  background: var(--bc-paper);
  border-right: 1px solid var(--bc-line);
  text-decoration: none;
  text-align: left;
  font-family: var(--bc-serif);
  line-height: 1.05;
}
.bc-brand strong { display: block; color: var(--bc-green-950); font-size: 23px; letter-spacing: 0.02em; }
.bc-brand span { display: block; margin-top: 3px; color: var(--bc-copy); font-size: 14px; }

.bc-main-nav {
  display: flex;
  align-items: stretch;
  gap: 4px;
  padding: 0 18px;
}
.bc-main-nav a {
  position: relative;
  display: grid;
  place-items: center;
  min-width: 84px;
  padding: 8px 12px;
  color: var(--bc-copy);
  text-decoration: none;
  font-size: 14px;
  font-weight: 650;
}
.bc-main-nav a:hover { background: var(--bc-green-50); }
.bc-main-nav a[aria-current="page"]::after {
  position: absolute;
  right: 12px;
  bottom: 0;
  left: 12px;
  height: 3px;
  content: "";
  background: var(--bc-green-900);
}

.bc-top-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 0 18px;
  border-left: 1px solid var(--bc-line);
}
.bc-language {
  display: inline-flex;
  padding: 2px;
  background: #edf1f0;
  border-radius: 7px;
}
.bc-language button {
  min-width: 42px;
  padding: 6px 9px;
  border: 0;
  border-radius: 5px;
  background: transparent;
  cursor: pointer;
  font-size: 12px;
  font-weight: 700;
}
.bc-language button.is-active { color: #fff; background: var(--bc-green-900); }

.bc-shell { width: min(1440px, 100%); margin: 0 auto; padding: 28px 30px 76px; }
.bc-page-head {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 28px;
  margin-bottom: 20px;
}
.bc-page-head h1 {
  margin: 0;
  color: var(--bc-ink);
  font: 400 clamp(30px, 4vw, 48px)/1.1 var(--bc-serif);
  letter-spacing: -0.025em;
}
.bc-page-head p { max-width: 760px; margin: 7px 0 0; color: var(--bc-muted); }
.bc-page-actions { display: flex; flex-wrap: wrap; justify-content: flex-end; gap: 9px; }
.bc-zh { display: block; color: var(--bc-muted); font-size: 0.91em; }
html[data-lang="en"] .bc-zh { display: none; }

.bc-btn {
  display: inline-flex;
  min-height: 40px;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 9px 16px;
  color: var(--bc-ink);
  background: var(--bc-paper);
  border: 1px solid var(--bc-line-dark);
  border-radius: 6px;
  text-decoration: none;
  cursor: pointer;
  font-size: 13px;
  font-weight: 750;
}
.bc-btn:hover { border-color: var(--bc-green-800); background: var(--bc-green-50); }
.bc-btn:disabled { cursor: not-allowed; opacity: 0.5; }
.bc-btn-primary { color: #fff; background: var(--bc-green-900); border-color: var(--bc-green-900); }
.bc-btn-primary:hover { color: #fff; background: var(--bc-green-950); }
.bc-btn-danger { color: var(--bc-red); border-color: #e0abb0; }
.bc-btn-small { min-height: 34px; padding: 6px 11px; font-size: 12px; }
.bc-icon-btn { width: 40px; padding: 8px; }

.bc-card { background: var(--bc-paper); border: 1px solid var(--bc-line); border-radius: var(--bc-radius); box-shadow: var(--bc-shadow); }
.bc-panel-heading { margin: 0; color: var(--bc-ink); font: 400 22px/1.2 var(--bc-serif); }
.bc-label { color: var(--bc-muted); font-size: 11px; font-weight: 800; letter-spacing: 0.06em; text-transform: uppercase; }
.bc-meta { color: var(--bc-muted); font-size: 12px; }

.bc-stat-grid { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); gap: 1px; margin-bottom: 18px; overflow: hidden; border: 1px solid var(--bc-line); border-radius: var(--bc-radius); background: var(--bc-line); }
.bc-stat { min-height: 110px; padding: 19px 20px; background: var(--bc-paper); }
.bc-stat strong { display: block; color: var(--bc-ink); font: 400 34px/1 var(--bc-serif); }
.bc-stat span { display: block; margin-top: 8px; color: var(--bc-muted); font-size: 12px; }

.bc-status {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 8px;
  color: var(--bc-green-900);
  background: var(--bc-green-50);
  border: 1px solid #a8cfc2;
  border-radius: 999px;
  font-size: 11px;
  font-weight: 750;
}
.bc-status::before { width: 7px; height: 7px; content: ""; background: currentColor; border-radius: 50%; }
.bc-status-warning { color: var(--bc-amber); background: var(--bc-amber-soft); border-color: #efcf8e; }
.bc-status-danger { color: var(--bc-red); background: var(--bc-red-soft); border-color: #eeaab1; }
.bc-status-muted { color: var(--bc-muted); background: #f1f3f3; border-color: var(--bc-line); }

.bc-quiz-layout {
  display: grid;
  grid-template-columns: 230px minmax(480px, 1fr) 300px;
  min-height: calc(100vh - 69px);
  background: var(--bc-paper);
}
.bc-route-rail { border-right: 1px solid var(--bc-line); background: #fbfcfc; }
.bc-route-head { display: flex; align-items: center; justify-content: space-between; min-height: 60px; padding: 14px 18px; border-bottom: 1px solid var(--bc-line); }
.bc-route-head strong { color: var(--bc-ink); font-size: 13px; }
.bc-route-list { display: grid; gap: 2px; padding: 12px; }
.bc-route-item {
  display: grid;
  grid-template-columns: 28px 1fr;
  align-items: center;
  gap: 9px;
  width: 100%;
  min-height: 44px;
  padding: 6px 8px;
  background: transparent;
  border: 1px solid transparent;
  border-radius: 5px;
  cursor: pointer;
  text-align: left;
}
.bc-route-item:hover { background: var(--bc-green-50); }
.bc-route-item.is-current { background: #f3faf7; border-color: var(--bc-green-800); }
.bc-route-item.is-locked { cursor: default; }
.bc-route-number { display: grid; width: 26px; height: 26px; place-items: center; border: 1px solid var(--bc-line-dark); border-radius: 50%; color: var(--bc-muted); font-size: 11px; font-weight: 800; }
.bc-route-item.is-current .bc-route-number { color: #fff; background: var(--bc-green-900); border-color: var(--bc-green-900); }
.bc-route-item.is-correct .bc-route-number { color: #fff; background: var(--bc-green-800); border-color: var(--bc-green-800); }
.bc-route-item.is-wrong .bc-route-number { color: #fff; background: var(--bc-red); border-color: var(--bc-red); }
.bc-route-copy strong { display: block; color: var(--bc-ink); font-size: 12px; }
.bc-route-copy span { display: block; color: var(--bc-muted); font-size: 10px; }
.bc-route-legend { margin: 12px 18px; padding-top: 14px; border-top: 1px solid var(--bc-line); color: var(--bc-muted); font-size: 11px; }
.bc-route-legend #route-audit { display: block; margin-top: 7px; color: var(--bc-green-800); font-family: var(--bc-mono); font-size: 10px; }

.bc-question-stage { min-width: 0; }
.bc-question-meta {
  display: grid;
  grid-template-columns: 1.1fr 0.55fr 0.75fr 1.2fr;
  min-height: 60px;
  border-bottom: 1px solid var(--bc-line);
}
.bc-question-meta > div { padding: 10px 20px; border-right: 1px solid var(--bc-line); }
.bc-question-meta span { display: block; color: var(--bc-muted); font-size: 10px; }
.bc-question-meta strong { display: block; margin-top: 2px; color: var(--bc-ink); font-family: var(--bc-serif); font-size: 14px; }
.bc-question-main { max-width: 900px; margin: 0 auto; padding: clamp(26px, 4vw, 52px) clamp(22px, 5vw, 58px) 120px; }
.bc-question-number { margin: 0 0 16px; color: var(--bc-muted); font-size: 12px; font-weight: 800; letter-spacing: 0.04em; }
.bc-question-stem { color: #172a32; font: 400 clamp(18px, 2vw, 22px)/1.65 var(--bc-serif); }
.bc-question-stem .katex { font-size: 1.08em; }
.bc-question-stem .native-question-figure { max-width: 760px; margin: 22px auto; padding: 12px; border: 1px solid var(--bc-line); background: #fff; }
.bc-question-stem .native-question-figure svg { display: block; width: 100%; height: auto; }
.bc-question-stem .native-question-figure figcaption { padding-top: 8px; color: var(--bc-muted); font: 600 13px/1.4 var(--bc-sans); text-align: center; }
.bc-question-stem :is(ol, ul) { margin: 14px 0 14px 28px; }
.bc-question-stem :is(ol, ul) li { margin: 8px 0; }
.bc-rich-table-wrap {
  max-width: 100%;
  margin: 16px 0;
  overflow-x: auto;
  border: 1px solid var(--bc-line-dark);
  border-radius: 6px;
  background: #fff;
}
.bc-data-table {
  width: 100%;
  min-width: max-content;
  border-collapse: collapse;
  color: var(--bc-ink);
  font: 500 14px/1.45 var(--bc-sans);
  font-variant-numeric: tabular-nums;
}
.bc-data-table th,
.bc-data-table td {
  min-width: 74px;
  padding: 10px 13px;
  border-right: 1px solid var(--bc-line);
  border-bottom: 1px solid var(--bc-line);
  text-align: center;
  white-space: nowrap;
}
.bc-data-table th { background: #f2f5f2; color: var(--bc-green-950); font-weight: 800; }
.bc-data-table tr:last-child > * { border-bottom: 0; }
.bc-data-table tr > *:last-child { border-right: 0; }
.bc-options { display: grid; gap: 7px; margin-top: 22px; }
.bc-option {
  display: grid;
  grid-template-columns: 34px 1fr auto;
  align-items: center;
  gap: 10px;
  width: 100%;
  min-height: 50px;
  padding: 8px 14px;
  background: #fff;
  border: 1px solid var(--bc-line-dark);
  border-radius: 5px;
  cursor: pointer;
  text-align: left;
  font-family: var(--bc-serif);
  font-size: 16px;
}
.bc-option:hover { border-color: var(--bc-green-800); }
.bc-option[aria-pressed="true"] { background: var(--bc-green-50); border-color: var(--bc-green-800); box-shadow: inset 3px 0 var(--bc-green-800); }
.bc-option.is-correct { background: var(--bc-green-50); border-color: var(--bc-green-800); }
.bc-option.is-wrong { background: var(--bc-red-soft); border-color: #e46d77; }
.bc-option-letter { display: grid; width: 29px; height: 29px; place-items: center; border: 1px solid var(--bc-line-dark); border-radius: 50%; font-family: var(--bc-sans); font-size: 12px; font-weight: 800; }
.bc-option-state { color: var(--bc-muted); font: 700 10px var(--bc-sans); }

.bc-question-tools { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 10px; margin-top: 12px; }
.bc-confidence { display: flex; align-items: center; gap: 6px; }
.bc-confidence button { width: 36px; height: 34px; padding: 0; background: #fff; border: 1px solid var(--bc-line); cursor: pointer; font-size: 12px; }
.bc-confidence button:first-of-type { border-radius: 5px 0 0 5px; }
.bc-confidence button:last-of-type { border-radius: 0 5px 5px 0; }
.bc-confidence button.is-active { color: #fff; background: var(--bc-green-900); border-color: var(--bc-green-900); }
.bc-scratchpad { margin-top: 11px; padding: 14px; background: #f3faf7; border: 1px solid #c9ded6; border-radius: 6px; }
.bc-scratchpad label { display: flex; justify-content: space-between; color: var(--bc-ink); font-size: 12px; font-weight: 800; }
.bc-scratchpad textarea { width: 100%; min-height: 90px; margin-top: 8px; padding: 10px; resize: vertical; background: transparent; border: 0; outline: 0; font-family: var(--bc-mono); font-size: 13px; line-height: 1.65; }
.bc-feedback { margin-top: 14px; overflow: hidden; border: 1px solid var(--bc-line); border-radius: 6px; }
.bc-feedback-row { display: grid; grid-template-columns: 170px 1fr; gap: 10px; padding: 12px 14px; border-bottom: 1px solid var(--bc-line); }
.bc-feedback-row:last-child { border-bottom: 0; }
.bc-feedback-row strong { color: var(--bc-ink); font-size: 13px; }
.bc-feedback-row p { margin: 0; font-family: var(--bc-serif); }
.bc-feedback-row.is-error { background: var(--bc-red-soft); border-color: #efc3c6; }
.bc-feedback-row.is-hint { background: var(--bc-amber-soft); }
.bc-feedback-row.is-next { background: var(--bc-blue-soft); }

.bc-evidence-rail { padding: 20px; border-left: 1px solid var(--bc-line); background: #fbfcfc; }
.bc-evidence-rail h2 { margin: 0 0 15px; color: var(--bc-ink); font: 400 20px var(--bc-serif); }
.bc-evidence-block { margin-bottom: 12px; padding: 15px; background: #fff; border: 1px solid var(--bc-line); border-radius: 7px; }
.bc-evidence-block h3 { margin: 0 0 9px; color: var(--bc-ink); font-size: 13px; }
.bc-gauge { --value: 0deg; display: grid; width: 150px; height: 78px; margin: 5px auto 0; place-items: end center; overflow: hidden; }
.bc-gauge::before { grid-area: 1/1; width: 132px; height: 132px; content: ""; border-radius: 50%; background: conic-gradient(from 270deg, var(--bc-green-800) var(--value), #e7eae9 0 180deg, transparent 0); }
.bc-gauge-value { z-index: 1; grid-area: 1/1; align-self: end; padding-bottom: 4px; color: var(--bc-green-950); font: 400 31px var(--bc-serif); }
.bc-meter { height: 7px; overflow: hidden; background: #e7eae9; border-radius: 99px; }
.bc-meter > span { display: block; width: 0; height: 100%; background: var(--bc-green-800); border-radius: inherit; transition: width 240ms ease; }
.bc-tag-list { display: flex; flex-wrap: wrap; gap: 6px; }
.bc-tag { padding: 3px 8px; color: var(--bc-red); background: var(--bc-red-soft); border: 1px solid #ef9ba2; border-radius: 999px; font-size: 11px; }
.bc-reason { margin: 0; color: var(--bc-muted); font-size: 12px; }

.bc-bottom-nav {
  position: fixed;
  z-index: 25;
  right: 0;
  bottom: 0;
  left: 0;
  display: grid;
  grid-template-columns: 230px 1fr 300px;
  min-height: 58px;
  color: #fff;
  background: var(--bc-green-900);
}
.bc-bottom-nav > div { display: flex; align-items: center; justify-content: center; gap: 10px; padding: 8px 16px; border-right: 1px solid rgba(255, 255, 255, 0.2); }
.bc-bottom-nav .bc-btn { color: #fff; background: transparent; border-color: rgba(255, 255, 255, 0.6); }

.bc-diagnostic-intro { display: grid; grid-template-columns: minmax(0, 1.4fr) minmax(280px, 0.6fr); gap: 20px; }
.bc-diagnostic-copy { padding: clamp(28px, 5vw, 58px); }
.bc-diagnostic-copy h1 { max-width: 780px; margin: 0; color: var(--bc-ink); font: 400 clamp(36px, 5vw, 62px)/1.03 var(--bc-serif); }
.bc-diagnostic-copy p { max-width: 720px; margin: 19px 0; color: var(--bc-muted); font-size: 17px; }
.bc-diagnostic-facts { padding: 28px; color: #fff; background: var(--bc-green-900); }
.bc-diagnostic-facts h2 { margin: 0 0 22px; font: 400 25px var(--bc-serif); }
.bc-fact-list { margin: 0; padding: 0; list-style: none; }
.bc-fact-list li { display: grid; grid-template-columns: 36px 1fr; gap: 10px; padding: 15px 0; border-top: 1px solid rgba(255, 255, 255, 0.24); }
.bc-fact-list strong { font-family: var(--bc-serif); font-size: 24px; }
.bc-intro-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 24px; }
.bc-notice { padding: 12px 14px; color: #6c4a05; background: var(--bc-amber-soft); border: 1px solid #ebcf94; border-radius: 6px; font-size: 12px; }

.bc-results { max-width: 1000px; margin: 0 auto; }
.bc-results-hero { display: grid; grid-template-columns: 190px 1fr; gap: 28px; align-items: center; padding: 34px; }
.bc-score-ring { --score: 0deg; display: grid; width: 160px; height: 160px; place-items: center; border-radius: 50%; background: conic-gradient(var(--bc-green-800) var(--score), #e5ebe9 0); }
.bc-score-ring::before { grid-area: 1/1; width: 125px; height: 125px; content: ""; background: #fff; border-radius: 50%; }
.bc-score-ring strong { z-index: 1; grid-area: 1/1; color: var(--bc-ink); font: 400 36px var(--bc-serif); }
.bc-result-units { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1px; margin-top: 16px; overflow: hidden; background: var(--bc-line); border: 1px solid var(--bc-line); border-radius: 8px; }
.bc-result-unit { padding: 15px; background: #fff; }

.bc-toolbar { display: flex; flex-wrap: wrap; align-items: end; gap: 14px; padding: 14px 16px; border: 1px solid var(--bc-line); background: #fff; }
.bc-field { display: grid; gap: 5px; }
.bc-field label { color: var(--bc-muted); font-size: 11px; font-weight: 750; }
.bc-field select { min-height: 38px; min-width: 150px; padding: 6px 34px 6px 10px; color: var(--bc-ink); background: #fff; border: 1px solid var(--bc-line-dark); border-radius: 5px; }

.bc-progress-grid { display: grid; grid-template-columns: minmax(0, 1.8fr) minmax(280px, 0.9fr); border: 1px solid var(--bc-line); background: #fff; }
.bc-mastery-map { min-width: 0; overflow-x: auto; border-right: 1px solid var(--bc-line); }
.bc-mastery-map h2, .bc-unit-detail h2 { margin: 0; padding: 14px 16px; color: var(--bc-ink); border-bottom: 1px solid var(--bc-line); font-size: 13px; }
.bc-map-table { width: 100%; min-width: 700px; border-collapse: collapse; text-align: center; }
.bc-map-table th, .bc-map-table td { height: 44px; padding: 7px; border-right: 1px solid var(--bc-line); border-bottom: 1px solid var(--bc-line); font-size: 11px; }
.bc-map-table th:first-child { width: 140px; padding-left: 14px; text-align: left; }
.bc-map-cell { background: transparent; border: 0; cursor: pointer; }
.bc-map-mark { display: inline-grid; width: 18px; height: 18px; place-items: center; color: var(--bc-muted); border: 1.5px solid currentColor; }
.bc-map-mark.Foundation { border-radius: 50%; }
.bc-map-mark.Standard { border-radius: 1px; }
.bc-map-mark.Stretch { transform: rotate(45deg) scale(0.75); }
.bc-map-mark.is-secure { color: #2c7b43; background: #e9f5eb; }
.bc-map-mark.is-developing { color: #c37c00; background: #fff5d9; }
.bc-map-mark.is-support { color: var(--bc-red); background: var(--bc-red-soft); }
.bc-unit-detail { min-width: 0; }
.bc-unit-detail-body { padding: 18px; }
.bc-level-row { display: grid; grid-template-columns: 90px 1fr 48px; gap: 11px; align-items: center; padding: 12px 0; border-bottom: 1px solid var(--bc-line); }
.bc-level-symbol { display: flex; align-items: center; gap: 8px; color: var(--bc-ink); font-size: 12px; font-weight: 750; }

.bc-mistake-section { margin-top: 16px; background: #fff; border: 1px solid var(--bc-line); }
.bc-tabs { display: flex; overflow-x: auto; border-bottom: 1px solid var(--bc-line); }
.bc-tab { padding: 13px 18px; background: transparent; border: 0; border-bottom: 3px solid transparent; cursor: pointer; color: var(--bc-muted); font-size: 12px; font-weight: 750; white-space: nowrap; }
.bc-tab.is-active { color: var(--bc-green-900); border-bottom-color: var(--bc-green-900); }
.bc-table-wrap { overflow-x: auto; }
.bc-mistake-table { width: 100%; min-width: 860px; border-collapse: collapse; }
.bc-mistake-table th { padding: 10px 12px; color: var(--bc-muted); background: #fbfcfc; border-bottom: 1px solid var(--bc-line); text-align: left; font-size: 10px; letter-spacing: 0.04em; text-transform: uppercase; }
.bc-mistake-table td { padding: 12px; border-bottom: 1px solid var(--bc-line); font-size: 12px; vertical-align: top; }
.bc-mistake-row { cursor: pointer; }
.bc-mistake-row:hover, .bc-mistake-row.is-selected { background: var(--bc-green-50); }
.bc-confidence-dot { display: inline-block; width: 8px; height: 8px; margin-right: 5px; border-radius: 50%; background: var(--bc-amber); }
.bc-mistake-detail { padding: 18px; border-top: 1px solid var(--bc-line); background: #fbfcfc; }
.bc-recovery-grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 1px; overflow: hidden; border: 1px solid var(--bc-line); background: var(--bc-line); }
.bc-recovery-column { min-height: 220px; padding: 16px; background: #fff; }
.bc-recovery-column h3 { margin: 0 0 12px; color: var(--bc-ink); font: 400 17px var(--bc-serif); }
.bc-recovery-column p, .bc-recovery-column li { color: var(--bc-muted); font-size: 12px; }
.bc-recovery-column ol, .bc-recovery-column ul { padding-left: 18px; }
.bc-empty { padding: 42px 20px; color: var(--bc-muted); text-align: center; }
.bc-data-note { margin-top: 14px; color: var(--bc-muted); font-size: 11px; }

.bc-loading { display: grid; min-height: 320px; place-items: center; color: var(--bc-muted); }
.bc-loading::before { width: 24px; height: 24px; margin-right: 9px; content: ""; border: 2px solid var(--bc-line); border-top-color: var(--bc-green-800); border-radius: 50%; animation: bc-spin 0.8s linear infinite; }
@keyframes bc-spin { to { transform: rotate(360deg); } }

.bc-math-source { padding: 1px 3px; color: var(--bc-ink); background: #f2f4f3; border-radius: 3px; font-family: var(--bc-serif); }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

@media (max-width: 1120px) {
  .bc-topbar { grid-template-columns: 150px 1fr auto; }
  .bc-main-nav a { min-width: auto; padding-right: 9px; padding-left: 9px; }
  .bc-quiz-layout { grid-template-columns: 180px minmax(430px, 1fr) 250px; }
  .bc-bottom-nav { grid-template-columns: 180px 1fr 250px; }
  .bc-recovery-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 900px) {
  .bc-topbar { position: relative; grid-template-columns: 140px 1fr; }
  .bc-top-actions { grid-column: 1 / -1; justify-content: flex-end; min-height: 48px; border-top: 1px solid var(--bc-line); }
  .bc-main-nav { overflow-x: auto; }
  .bc-shell { padding: 22px 18px 66px; }
  .bc-stat-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .bc-quiz-layout { display: block; min-height: auto; }
  .bc-route-rail { border-right: 0; border-bottom: 1px solid var(--bc-line); }
  .bc-route-list { display: flex; overflow-x: auto; }
  .bc-route-item { min-width: 138px; }
  .bc-route-legend { display: none; }
  .bc-evidence-rail { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; border-top: 1px solid var(--bc-line); border-left: 0; }
  .bc-evidence-rail h2 { grid-column: 1 / -1; }
  .bc-bottom-nav { position: sticky; grid-template-columns: repeat(3, 1fr); }
  .bc-diagnostic-intro { grid-template-columns: 1fr; }
  .bc-progress-grid { grid-template-columns: 1fr; }
  .bc-mastery-map { border-right: 0; border-bottom: 1px solid var(--bc-line); }
}

@media (max-width: 640px) {
  .bc-topbar { display: block; }
  .bc-brand { min-height: 58px; }
  .bc-main-nav { min-height: 48px; padding: 0 8px; border-bottom: 1px solid var(--bc-line); }
  .bc-main-nav a { min-width: max-content; font-size: 12px; }
  .bc-top-actions { min-height: 44px; padding: 0 10px; }
  .bc-page-head { display: block; }
  .bc-page-actions { justify-content: flex-start; margin-top: 15px; }
  .bc-stat-grid { display: grid; grid-template-columns: 1fr 1fr; }
  .bc-stat { min-height: 92px; padding: 15px; }
  .bc-stat:last-child { grid-column: 1 / -1; }
  .bc-question-meta { grid-template-columns: 1fr 1fr; }
  .bc-question-meta > div:nth-child(2) { border-right: 0; }
  .bc-question-meta > div:nth-child(-n+2) { border-bottom: 1px solid var(--bc-line); }
  .bc-question-main { padding: 26px 15px 64px; }
  .bc-question-tools { align-items: stretch; flex-direction: column; }
  .bc-confidence { justify-content: space-between; }
  .bc-feedback-row { grid-template-columns: 1fr; }
  .bc-evidence-rail { display: block; padding: 16px; }
  .bc-bottom-nav { grid-template-columns: 1fr 1fr; }
  .bc-bottom-nav > div:nth-child(2) { display: none; }
  .bc-results-hero { grid-template-columns: 1fr; text-align: center; }
  .bc-score-ring { margin: 0 auto; }
  .bc-result-units { grid-template-columns: 1fr; }
  .bc-toolbar { align-items: stretch; flex-direction: column; }
  .bc-field select { width: 100%; }
  .bc-recovery-grid { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; }
}

:focus-visible { outline: 3px solid #45a889; outline-offset: 2px; }

.bc-mistake-analysis{margin-top:14px;padding:18px;border:1px solid #c9d3cd;border-left:4px solid var(--bc-rust,#a7533f);border-radius:8px;background:#fffdfa}
.bc-mistake-analysis[hidden]{display:none}
.bc-mistake-analysis-head{display:flex;align-items:flex-start;justify-content:space-between;gap:18px}
.bc-mistake-analysis h2{margin:3px 0 10px;color:var(--bc-ink);font:600 clamp(21px,2.2vw,28px)/1.2 var(--bc-serif)}
.bc-mistake-permission-note{margin:12px 0;padding:11px 12px;border:1px solid #d8ddd9;background:#f6f4ee;color:var(--bc-muted);font-size:13px;line-height:1.55}
.bc-mistake-actions{display:flex;flex-wrap:wrap;gap:9px;margin-top:12px}
.bc-photo-fallback{color:var(--bc-muted);font-size:13px}
.bc-photo-fallback summary{cursor:pointer;padding:8px 0}
.bc-photo-fallback[open] .bc-btn{margin-top:8px}
.bc-mistake-analysis-result{margin-top:13px;padding-top:4px;border-top:1px solid #d8ddd9}
.bc-mistake-analysis-result p{margin:10px 0;line-height:1.6}
@media(max-width:700px){.bc-mistake-analysis{padding:15px}.bc-mistake-analysis-head{display:block}.bc-mistake-actions,.bc-photo-fallback{width:100%}.bc-mistake-actions .bc-btn{width:100%;justify-content:center}}