:root {
  color-scheme: light;
  --bg: #f5f2ea;
  --paper: #fffdf8;
  --ink: #202124;
  --muted: #64625d;
  --line: #ded8ca;
  --accent: #2f6f6a;
  --dark-square: #779954;
  --light-square: #ebecd0;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  touch-action: manipulation;
  font-family: "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  color: var(--ink);
  background: var(--bg);
}

a { color: inherit; }

.chapter-list {
  position: fixed;
  inset: 0 auto 0 0;
  width: 260px;
  overflow: auto;
  border-right: 1px solid var(--line);
  background: #ede7d9;
  padding: 16px;
}

.chapter-list nav {
  display: grid;
  gap: 3px;
}

.chapter-list a {
  display: block;
  border-radius: 6px;
  padding: 7px 9px;
  text-decoration: none;
  color: #38352f;
  font-size: 13px;
  line-height: 1.25;
}

.chapter-list a:hover,
.chapter-list a[aria-current="page"] {
  background: #d9ceba;
}

.home-link {
  margin-bottom: 12px;
  font-weight: 700;
}

.page-shell {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 390px;
  gap: 24px;
  margin-left: 260px;
  padding: 24px;
}

.lesson-panel,
.viewer-panel,
.index-page {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 14px 40px rgba(70, 55, 25, 0.08);
}

.lesson-panel {
  min-width: 0;
  padding: 34px;
  line-height: 1.72;
}

.lesson-panel h1 {
  margin-top: 0;
  font-size: 32px;
  line-height: 1.18;
}

.lesson-panel h2,
.lesson-panel h3 {
  margin-top: 34px;
  line-height: 1.28;
}

.lesson-panel p {
  margin: 13px 0;
}

.lesson-panel table {
  width: 100%;
  border-collapse: collapse;
  margin: 18px 0;
  font-size: 14px;
}

.lesson-panel td {
  border: 1px solid var(--line);
  padding: 6px 8px;
}

.lesson-panel img {
  max-width: 100%;
}

.viewer-panel {
  min-width: 0;
  padding: 16px;
}

.viewer-sticky {
  position: sticky;
  top: 16px;
}

.viewer-heading {
  display: grid;
  gap: 10px;
  margin-bottom: 14px;
}

.viewer-heading h2 {
  margin: 0;
  font-size: 18px;
}

select,
button {
  min-height: 38px;
  border: 1px solid #bcb39f;
  border-radius: 6px;
  background: #fffaf0;
  color: var(--ink);
  font: inherit;
  font-size: 16px;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
}

button {
  cursor: pointer;
  font-weight: 700;
}

button:hover {
  border-color: var(--accent);
}

.board-host {
  width: min(100%, 356px);
  aspect-ratio: 1;
  margin-inline: auto;
}

.board-host .board-b72b1 {
  border: 2px solid #423f38;
  box-shadow: 0 8px 22px rgba(56, 50, 38, 0.18);
}

.board-host .white-1e1d7 {
  background-color: var(--light-square);
}

.board-host .black-3c85d {
  background-color: var(--dark-square);
}

.board-host .highlight-square {
  box-shadow: inset 0 0 0 4px rgba(242, 203, 83, 0.82);
}

.viewer-controls {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
  margin-top: 14px;
}

.move-list {
  max-height: 220px;
  overflow: auto;
  margin: 14px 0 0;
  padding-left: 28px;
  font-size: 14px;
}

.move-list li {
  padding: 4px 6px;
  border-radius: 5px;
}

.move-list li.current {
  background: #d7ebe7;
  color: #143c38;
  font-weight: 700;
}

.viewer-status {
  min-height: 22px;
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 13px;
}

.index-page {
  max-width: 980px;
  margin: 32px auto;
  padding: 34px;
}

.index-page h1 {
  margin-top: 0;
}

.index-list {
  columns: 2;
  gap: 28px;
  padding-left: 0;
  list-style: none;
}

.index-list li {
  break-inside: avoid;
  margin: 0 0 7px;
}

.index-list a {
  display: flex;
  gap: 10px;
  padding: 8px 10px;
  border-radius: 6px;
  text-decoration: none;
}

.index-list a:hover {
  background: #eee6d7;
}

.index-list span {
  color: var(--accent);
  font-weight: 800;
  min-width: 34px;
}

@media (max-width: 1100px) {
  .chapter-list {
    position: static;
    width: auto;
    max-height: 210px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .page-shell {
    margin-left: 0;
    grid-template-columns: 1fr;
  }

  .viewer-sticky {
    position: static;
  }
}

@media (max-width: 720px) {
  .page-shell {
    padding: 12px;
    gap: 12px;
  }

  .lesson-panel {
    padding: 20px;
    line-height: 1.66;
    order: 2;
  }

  .lesson-panel h1 {
    font-size: 25px;
  }

  .viewer-panel {
    order: 1;
    padding: 12px;
  }

  .viewer-heading {
    gap: 8px;
    margin-bottom: 10px;
  }

  .viewer-controls {
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 6px;
  }

  .move-list {
    display: flex;
    gap: 6px;
    max-height: none;
    overflow-x: auto;
    padding: 0 0 4px;
    list-style: none;
  }

  .move-list li {
    flex: 0 0 auto;
  }

  .index-list {
    columns: 1;
  }
}