:root {
  --bg: #f7f4ee;
  --paper: #fffdf8;
  --paper-strong: #ffffff;
  --ink: #24231f;
  --muted: #6f6a60;
  --line: rgba(36, 35, 31, 0.13);
  --code: #171b1f;
  --code-ink: #edf3f8;
  --teal: #127a76;
  --blue: #315f9e;
  --amber: #b46a00;
  --red: #a53f3f;
  --shadow: 0 18px 50px rgba(48, 40, 24, 0.10);
}

html[data-theme="dark"] {
  --bg: #101315;
  --paper: #171b1d;
  --paper-strong: #1e2427;
  --ink: #f2eee6;
  --muted: #b5ada0;
  --line: rgba(242, 238, 230, 0.14);
  --code: #080a0c;
  --code-ink: #eaf1f6;
  --teal: #5fc5bd;
  --blue: #91b8ee;
  --amber: #e0a14b;
  --red: #ee8989;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.28);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.68;
}

a { color: var(--teal); text-decoration: none; }
a:hover, a:focus-visible { text-decoration: underline; }

.skip-link {
  position: fixed;
  top: 10px;
  left: 10px;
  transform: translateY(-140%);
  background: var(--ink);
  color: var(--paper);
  padding: 8px 12px;
  z-index: 100;
}
.skip-link:focus { transform: translateY(0); }

.reading-progress {
  position: fixed;
  inset: 0 0 auto 0;
  height: 3px;
  background: transparent;
  z-index: 90;
}
.reading-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--teal), var(--amber), var(--blue));
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  min-height: 58px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 12px clamp(18px, 4vw, 48px);
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: blur(14px);
}
.brand { color: var(--ink); font-weight: 760; }
.module-nav { display: flex; gap: 10px; flex-wrap: wrap; }
.module-nav a {
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 5px 10px;
  font-size: 0.9rem;
  background: var(--paper-strong);
}

.lecture {
  width: min(1040px, calc(100% - 36px));
  margin: 0 auto;
  padding: 44px 0 88px;
}

.paper-header {
  padding: 42px 0 30px;
  border-bottom: 1px solid var(--line);
}
.kicker {
  margin: 0 0 10px;
  color: var(--amber);
  text-transform: uppercase;
  letter-spacing: 0;
  font-size: 0.82rem;
  font-weight: 760;
}
.paper-header h1 {
  margin: 0;
  font-size: clamp(2.2rem, 6vw, 4.8rem);
  line-height: 1.05;
  letter-spacing: 0;
}
.subtitle {
  margin: 18px 0 0;
  max-width: 780px;
  color: var(--muted);
  font-size: 1.08rem;
}

.chapter {
  padding: 48px 0;
  border-bottom: 1px solid var(--line);
}
.chapter-header {
  display: grid;
  gap: 8px;
  margin-bottom: 22px;
}
.chapter h2 {
  margin: 0;
  font-size: clamp(1.65rem, 3vw, 2.5rem);
  line-height: 1.18;
  letter-spacing: 0;
}
.chapter h3 { margin: 0 0 10px; font-size: 1.16rem; }
.chapter h4 { margin: 18px 0 8px; font-size: 1rem; }
.chapter p, .chapter li { color: var(--muted); }
.chapter-summary { margin: 0; max-width: 820px; }

.overview-panel,
.judgement-card {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 22px;
  box-shadow: var(--shadow);
}
.visual-copy p { margin-bottom: 0; }
.route-grid {
  margin-top: 18px;
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 8px;
}
.route-grid span {
  min-height: 44px;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper-strong);
  color: var(--ink);
  font-weight: 680;
  font-size: 0.9rem;
  text-align: center;
}

.toolbar {
  margin-top: 22px;
  display: grid;
  grid-template-columns: minmax(220px, 1.2fr) minmax(160px, 0.6fr) minmax(140px, 0.45fr) auto;
  gap: 12px;
  align-items: end;
}
.toolbar label {
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 0.88rem;
  font-weight: 700;
}
.toolbar input,
.toolbar select {
  width: 100%;
  min-height: 42px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper-strong);
  color: var(--ink);
  padding: 8px 10px;
  font: inherit;
}
.toolbar-actions { display: flex; gap: 8px; flex-wrap: wrap; }
.toolbar button,
.copy-code,
.toc-toggle {
  min-height: 42px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper-strong);
  color: var(--ink);
  padding: 8px 12px;
  font: inherit;
  font-weight: 720;
  cursor: pointer;
}
.toolbar button:hover,
.copy-code:hover,
.toc-toggle:hover { border-color: var(--teal); color: var(--teal); }
.result-count { margin: 12px 0 0; color: var(--muted); }

.problem-list { display: grid; gap: 12px; min-width: 0; }
.problem-group { min-width: 0; }
.problem-card {
  min-width: 0;
  max-width: 100%;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow: clip;
}
.problem-card[hidden], .problem-group[hidden] { display: none; }
.problem-card summary {
  list-style: none;
  cursor: pointer;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 12px;
  align-items: center;
  padding: 16px 18px;
}
.problem-card summary::-webkit-details-marker { display: none; }
.problem-card summary:hover { background: color-mix(in srgb, var(--teal) 7%, transparent); }
.problem-title {
  min-width: 0;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 10px;
  color: var(--ink);
  font-weight: 780;
}
.problem-id {
  min-width: 44px;
  color: var(--teal);
  font-variant-numeric: tabular-nums;
}
.problem-meta {
  min-width: 0;
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: end;
  color: var(--muted);
  font-size: 0.88rem;
}
.problem-meta span,
.problem-links span,
.problem-links a {
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 3px 8px;
  background: var(--paper-strong);
}
.problem-body {
  min-width: 0;
  max-width: 100%;
  padding: 0 18px 18px;
  border-top: 1px solid var(--line);
}
.problem-links {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin: 16px 0;
  color: var(--muted);
  font-size: 0.88rem;
}
.solution-block {
  min-width: 0;
  margin-top: 18px;
  padding-top: 8px;
  border-top: 1px dashed var(--line);
}
.complexity { margin-bottom: 0; }
.spec-list,
.analysis-list,
.complexity-list,
.constraint-box ul {
  margin: 10px 0 0;
  padding-left: 1.2rem;
}
.spec-list p,
.analysis-list li,
.complexity-list li,
.constraint-box li {
  margin: 7px 0;
  color: color-mix(in srgb, var(--ink) 86%, var(--muted));
}
.constraint-box {
  margin: 12px 0;
  padding: 12px 14px;
  border: 1px solid color-mix(in srgb, var(--teal) 22%, var(--line));
  border-radius: 8px;
  background: color-mix(in srgb, var(--teal) 8%, var(--paper-strong));
}
.constraint-box strong,
.spec-list strong,
.analysis-list strong,
.complexity-list strong {
  color: var(--ink);
}

.code-block {
  position: relative;
  min-width: 0;
  max-width: 100%;
  margin: 12px 0;
  border-radius: 8px;
  overflow: hidden;
  background: var(--code);
  border: 1px solid color-mix(in srgb, var(--line) 60%, transparent);
}
.copy-code {
  position: absolute;
  top: 10px;
  right: 10px;
  min-height: 32px;
  padding: 4px 10px;
  background: color-mix(in srgb, var(--code) 82%, white);
  color: var(--code-ink);
  border-color: rgba(255, 255, 255, 0.18);
  font-size: 0.82rem;
}
pre {
  margin: 0;
  padding: 18px;
  overflow: auto;
  max-width: 100%;
  max-height: 620px;
}
code {
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: 0.9rem;
  line-height: 1.56;
}
:not(pre) > code {
  color: var(--ink);
  background: color-mix(in srgb, var(--blue) 8%, var(--paper-strong));
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: 0.06rem 0.28rem;
  white-space: normal;
  overflow-wrap: anywhere;
}
pre code {
  color: var(--code-ink);
  background: transparent;
  border: 0;
  padding: 0;
  font-size: 0.88rem;
  white-space: pre;
}

.lecture-toc {
  display: none;
}
.toc-toggle {
  position: sticky;
  top: 72px;
  display: block;
  width: fit-content;
  margin: 12px 18px 0 auto;
  z-index: 70;
  box-shadow: var(--shadow);
}
.lecture-toc.open {
  display: block;
  position: fixed;
  z-index: 65;
  left: 16px;
  right: 16px;
  top: 128px;
  bottom: 18px;
  max-height: min(70vh, 620px);
  overflow: auto;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  box-shadow: var(--shadow);
}
.lecture-toc p {
  margin: 0 0 10px;
  color: var(--muted);
  font-weight: 780;
}
.lecture-toc nav { display: grid; gap: 4px; }
.lecture-toc a {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  color: var(--muted);
  padding: 7px 9px;
  border-radius: 8px;
  font-size: 0.9rem;
}
.lecture-toc a.active,
.lecture-toc a:hover,
.lecture-toc a:focus-visible {
  background: color-mix(in srgb, var(--teal) 12%, transparent);
  color: var(--teal);
  text-decoration: none;
}
.lecture-toc small { color: inherit; opacity: 0.72; }

@media (min-width: 1180px) {
  .lecture {
    width: min(1040px, calc(100vw - 360px));
    margin-left: 300px;
    margin-right: 40px;
  }
  .lecture-toc {
    display: block;
    position: fixed;
    left: 32px;
    top: 86px;
    bottom: 28px;
    width: 220px;
    overflow: auto;
    background: color-mix(in srgb, var(--paper) 92%, transparent);
    border: 1px solid var(--line);
    border-radius: 8px;
    padding: 14px;
    box-shadow: var(--shadow);
  }
  .toc-toggle { display: none; }
}

@media (max-width: 900px) {
  .site-header { align-items: flex-start; flex-direction: column; }
  .paper-header h1 { font-size: 2.4rem; }
  .toolbar { grid-template-columns: 1fr; }
  .route-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .problem-card summary { grid-template-columns: 1fr; }
  .problem-meta { justify-content: start; }
  pre { padding: 54px 14px 14px; }
  code { font-size: 0.82rem; }
}