:root {
  --wb-canvas: #f6f8fb;
  --wb-surface: #ffffff;
  --wb-soft: #eef3f8;
  --wb-action-soft: #eaf1ff;
  --wb-signal-soft: #dff4f1;
  --wb-text: #172033;
  --wb-reading: #28364a;
  --wb-muted: #5d6b7a;
  --wb-line: #dce4ed;
  --wb-line-strong: #c7d2df;
  --wb-action: #2164e8;
  --wb-action-hover: #1d56d8;
  --wb-signal: #0f8f8a;
  --wb-signal-dark: #0b746f;
  --wb-font: "Noto Sans KR", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  min-width: 320px;
  margin: 0;
  background: var(--wb-canvas);
  color: var(--wb-text);
  font-family: var(--wb-font);
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; }

.skip-link {
  position: fixed;
  z-index: 1000;
  top: 12px;
  left: 12px;
  padding: 10px 14px;
  border-radius: 10px;
  background: var(--wb-text);
  color: #fff;
  transform: translateY(-150%);
}
.skip-link:focus { transform: translateY(0); }

.global-nav {
  position: sticky;
  z-index: 30;
  top: 0;
  min-height: 64px;
  padding-inline: max(24px, calc((100% - 1240px) / 2));
  display: flex;
  align-items: center;
  border-bottom: 1px solid rgba(220, 228, 237, .9);
  background: rgba(255, 255, 255, .94);
  backdrop-filter: blur(16px) saturate(135%);
}

.nav-logo {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  gap: 9px;
  color: var(--wb-text);
  font-size: 17px;
  font-weight: 800;
  letter-spacing: -.03em;
  text-decoration: none;
}
.nav-mark { width: 24px; height: 24px; }
.nav-spacer { flex: 1; }
.nav-links { display: flex; align-items: center; gap: 6px; }
.workbook-nav-link {
  min-height: 44px;
  padding: 0 14px;
  display: inline-flex;
  align-items: center;
  border-radius: 10px;
  color: var(--wb-muted);
  font-size: 13px;
  font-weight: 700;
  text-decoration: none;
}
.workbook-nav-link:hover,
.workbook-nav-link[aria-current="page"] { background: var(--wb-action-soft); color: var(--wb-action); }

.workbook-shell {
  width: min(1120px, calc(100% - 48px));
  margin: 0 auto;
  padding: 90px 0 120px;
}

.workbook-cover {
  min-height: 320px;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: end;
  gap: 72px;
  border-bottom: 1px solid var(--wb-line-strong);
}
.workbook-cover > div { padding-bottom: 52px; }
.workbook-cover h1 {
  max-width: 760px;
  margin: 0;
  font-size: clamp(52px, 7vw, 86px);
  font-weight: 800;
  line-height: 1.06;
  letter-spacing: -.04em;
}
.workbook-cover p {
  max-width: 720px;
  margin: 28px 0 0;
  color: var(--wb-muted);
  font-size: 18px;
  line-height: 1.78;
}

.workbook-summary {
  min-width: 260px;
  margin: 0 0 52px;
  display: grid;
  gap: 0;
}
.workbook-summary > div {
  padding: 15px 0;
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 28px;
  border-top: 1px solid var(--wb-line);
}
.workbook-summary > div:last-child { border-bottom: 1px solid var(--wb-line); }
.workbook-summary dt { color: var(--wb-muted); font-size: 12px; font-weight: 650; }
.workbook-summary dd { margin: 0; color: var(--wb-text); font-size: 16px; font-weight: 760; }

.workbook-view-switch {
  margin-top: 34px;
  display: inline-flex;
  padding: 4px;
  border-radius: 12px;
  background: var(--wb-soft);
}
.workbook-view-switch a {
  min-height: 44px;
  padding: 0 18px;
  display: inline-flex;
  align-items: center;
  border-radius: 9px;
  color: var(--wb-muted);
  font-size: 13px;
  font-weight: 720;
  text-decoration: none;
}
.workbook-view-switch a[aria-current="page"] { background: var(--wb-surface); color: var(--wb-text); }

.workbook-boundary {
  max-width: 820px;
  margin: 22px 0 0;
  padding: 16px 18px;
  border: 0;
  border-radius: 12px;
  background: var(--wb-soft);
  color: var(--wb-muted);
  font-size: 13px;
  line-height: 1.75;
}

.workbook-controls {
  position: sticky;
  z-index: 20;
  top: 64px;
  margin-top: 54px;
  padding: 14px 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto auto;
  align-items: center;
  gap: 22px;
  border-bottom: 1px solid var(--wb-line);
  background: rgba(246, 248, 251, .96);
  backdrop-filter: blur(14px) saturate(130%);
}
.difficulty-filter { display: flex; align-items: center; gap: 5px; overflow-x: auto; }
.difficulty-filter button {
  min-width: 48px;
  min-height: 44px;
  padding: 0 13px;
  border: 0;
  border-radius: 10px;
  background: transparent;
  color: var(--wb-muted);
  font: 700 13px/1 var(--wb-font);
  white-space: nowrap;
  cursor: pointer;
}
.difficulty-filter button:hover { background: var(--wb-soft); color: var(--wb-text); }
.difficulty-filter button.is-active { background: var(--wb-action); color: #fff; }

.topic-filter { display: flex; align-items: center; gap: 9px; color: var(--wb-muted); font-size: 12px; font-weight: 650; white-space: nowrap; }
.topic-filter select {
  min-height: 44px;
  max-width: 220px;
  padding: 0 34px 0 12px;
  border: 1px solid var(--wb-line-strong);
  border-radius: 10px;
  background: var(--wb-surface);
  color: var(--wb-text);
  font: 650 13px/1 var(--wb-font);
}
.workbook-count { margin: 0; color: var(--wb-muted); font-size: 12px; white-space: nowrap; }

.workbook-content { margin-top: 78px; }
.workbook-topic { scroll-margin-top: 150px; }
.workbook-topic + .workbook-topic { margin-top: 112px; }
.workbook-topic[hidden] { display: none; }
.workbook-topic-header {
  padding-bottom: 28px;
  display: grid;
  grid-template-columns: 68px minmax(0, 1fr);
  gap: 18px;
  border-bottom: 1px solid var(--wb-line-strong);
}
.workbook-topic-number { color: var(--wb-action); font-size: 14px; font-weight: 800; font-variant-numeric: tabular-nums; }
.workbook-topic-header h2 { margin: 0; font-size: clamp(28px, 4vw, 42px); line-height: 1.25; letter-spacing: -.032em; }
.workbook-topic-header p { max-width: 760px; margin: 12px 0 0; color: var(--wb-muted); font-size: 15px; line-height: 1.75; }
.workbook-topic-guide {
  max-width: 760px;
  margin-top: 18px;
  border-top: 1px solid var(--wb-line);
}
.workbook-topic-guide summary {
  min-height: 44px;
  display: flex;
  align-items: center;
  color: var(--wb-action);
  font-size: 13px;
  font-weight: 720;
  cursor: pointer;
}
.workbook-topic-guide p {
  margin: 0 0 18px;
  white-space: pre-line;
}

.workbook-question {
  padding: 38px 0 42px 86px;
  scroll-margin-top: 150px;
  border-bottom: 1px solid var(--wb-line);
}
.workbook-question[hidden] { display: none; }
.workbook-question-meta { display: flex; align-items: center; gap: 10px; color: var(--wb-muted); font-size: 12px; }
.workbook-question-number { font-weight: 750; font-variant-numeric: tabular-nums; }
.workbook-level {
  min-height: 26px;
  padding: 0 9px;
  display: inline-flex;
  align-items: center;
  border-radius: 7px;
  background: var(--wb-soft);
  color: var(--wb-muted);
  font-weight: 700;
}
.workbook-level[data-level="최하"], .workbook-level[data-level="하"] { background: var(--wb-signal-soft); color: var(--wb-signal-dark); }
.workbook-level[data-level="상"], .workbook-level[data-level="최상"] { background: var(--wb-action-soft); color: var(--wb-action); }
.workbook-format { color: var(--wb-muted); }
.workbook-question h3 { max-width: 820px; margin: 18px 0 0; font-size: clamp(20px, 2.5vw, 27px); line-height: 1.56; letter-spacing: -.024em; }
.workbook-context {
  max-width: 820px;
  margin-top: 18px;
  padding: 16px 18px;
  border: 0;
  border-radius: 11px;
  background: var(--wb-soft);
  color: var(--wb-reading);
  font-size: 14px;
  line-height: 1.75;
  white-space: pre-line;
}
.workbook-prompt { max-width: 820px; margin-top: 20px; color: var(--wb-reading); font-size: 17px; line-height: 1.9; white-space: pre-line; }
.workbook-formula {
  max-width: 820px;
  margin-top: 22px;
  padding: 20px 24px;
  border-radius: 12px;
  background: var(--wb-soft);
  color: var(--wb-text);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-size: 17px;
  line-height: 1.75;
  white-space: pre-wrap;
}
.workbook-choices {
  max-width: 820px;
  margin: 24px 0 0;
  padding: 0;
  display: grid;
  gap: 0;
  border-block: 1px solid var(--wb-line);
  list-style: none;
}
.workbook-choices li {
  padding: 15px 0;
  border-radius: 0;
  background: transparent;
  color: var(--wb-reading);
  font-size: 15px;
  line-height: 1.65;
}
.workbook-choices li + li { border-top: 1px solid var(--wb-line); }

.workbook-answer {
  max-width: 820px;
  margin-top: 28px;
  padding: 20px 22px;
  border-radius: 12px;
  background: var(--wb-signal-soft);
  color: var(--wb-text);
}
.workbook-answer span { display: block; color: var(--wb-signal-dark); font-size: 11px; font-weight: 750; }
.workbook-answer strong { display: block; margin-top: 6px; font-size: 18px; line-height: 1.6; }
.workbook-solution { max-width: 820px; margin: 26px 0 0; padding: 0 0 0 22px; color: var(--wb-reading); }
.workbook-solution li { padding-left: 5px; font-size: 16px; line-height: 1.85; }
.workbook-solution li + li { margin-top: 10px; }
.workbook-distractors {
  max-width: 820px;
  margin-top: 22px;
  padding-top: 18px;
  border-top: 1px solid color-mix(in srgb, var(--wb-line) 72%, transparent);
}
.workbook-distractors summary {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  color: var(--wb-reading);
  font-size: 14px;
  font-weight: 720;
  cursor: pointer;
}
.workbook-distractors ol { margin: 8px 0 0; padding-left: 22px; }
.workbook-distractors li { padding-left: 5px; color: var(--wb-muted); font-size: 14px; line-height: 1.75; }
.workbook-distractors li + li { margin-top: 8px; }
.workbook-evidence {
  max-width: 820px;
  margin-top: 26px;
  padding-top: 22px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  border-top: 1px solid var(--wb-line);
}
.workbook-evidence h4 { margin: 0; color: var(--wb-muted); font-size: 11px; font-weight: 750; }
.workbook-evidence p { margin: 8px 0 0; color: var(--wb-muted); font-size: 13px; line-height: 1.75; }
.workbook-problem-link { margin-top: 24px; display: inline-flex; min-height: 44px; align-items: center; color: var(--wb-action); font-size: 13px; font-weight: 720; text-underline-offset: 4px; }

.workbook-error { margin: 56px 0; padding: 24px; border-radius: 12px; background: #fff1f2; color: #a92f3b; }
.workbook-footer {
  width: min(1120px, calc(100% - 48px));
  margin: 0 auto;
  padding: 36px 0 48px;
  display: flex;
  justify-content: space-between;
  gap: 36px;
  border-top: 1px solid var(--wb-line);
  color: var(--wb-muted);
  font-size: 12px;
}
.workbook-footer div { display: grid; gap: 6px; }
.workbook-footer strong { color: var(--wb-text); font-size: 15px; }
.workbook-footer nav { display: flex; align-items: center; gap: 20px; }
.workbook-footer a { min-height: 44px; display: inline-flex; align-items: center; color: var(--wb-muted); text-underline-offset: 4px; }

:where(button, select, a):focus-visible { outline: 3px solid var(--wb-signal); outline-offset: 3px; }

@media (max-width: 820px) {
  .global-nav { padding-inline: 16px; }
  .workbook-nav-link { display: none; }
  .workbook-shell { width: min(100% - 32px, 680px); padding-top: 58px; }
  .workbook-cover { min-height: 0; grid-template-columns: 1fr; gap: 36px; }
  .workbook-cover > div { padding-bottom: 0; }
  .workbook-cover h1 { font-size: clamp(46px, 13vw, 68px); }
  .workbook-cover p { font-size: 16px; }
  .workbook-summary { min-width: 0; margin-bottom: 38px; }
  .workbook-controls { grid-template-columns: 1fr auto; gap: 12px; }
  .difficulty-filter { grid-column: 1 / -1; }
  .topic-filter span { display: none; }
  .workbook-count { text-align: right; }
  .workbook-topic-header { grid-template-columns: 48px minmax(0, 1fr); }
  .workbook-question { padding-left: 66px; }
}

@media (max-width: 540px) {
  .workbook-shell, .workbook-footer { width: min(100% - 28px, 520px); }
  .workbook-shell { padding-bottom: 84px; }
  .workbook-view-switch { width: 100%; }
  .workbook-view-switch a { flex: 1; justify-content: center; }
  .workbook-controls { top: 56px; }
  .topic-filter { grid-column: 1 / -1; justify-content: space-between; }
  .topic-filter select { min-width: 0; width: 0; max-width: none; flex: 1; }
  .workbook-count { grid-column: 1 / -1; text-align: left; }
  .workbook-content { margin-top: 56px; }
  .workbook-topic + .workbook-topic { margin-top: 82px; }
  .workbook-topic-header { grid-template-columns: 1fr; gap: 10px; }
  .workbook-question { padding: 32px 0 36px; }
  .workbook-prompt { font-size: 16px; }
  .workbook-boundary { font-size: 12px; }
  .workbook-formula { padding: 17px 15px; font-size: 15px; overflow-x: auto; }
  .workbook-evidence { grid-template-columns: 1fr; gap: 18px; }
  .workbook-footer { align-items: flex-start; flex-direction: column; }
  .workbook-footer nav { align-items: flex-start; flex-direction: column; gap: 0; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}