/* Reversi. The top part is the shared paper-and-ink look of the other sections (copied from
   ../hangman/styles.css: header, intro, tabs, buttons, article, footer); the board and the diagrams are at the bottom. */
:root {
  --paper: #faf8f2;
  --ink: #292d28;
  --muted: #697064;
  --line: #dfdfd3;
  --accent: #bd5f3e;
  --teal: #24878b;
  --pad: #fffdf8;
  --dot: #d5d3c4;
  --ink-mark: #bd5f3e;
  --display: ui-rounded, "SF Pro Rounded", "Hiragino Maru Gothic ProN", "Arial Rounded MT Bold", system-ui, sans-serif;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #1b1d1a; --ink: #ecebe3; --muted: #a3a898; --line: #3a3d36;
    --accent: #e27f5a; --teal: #58b9bd; --pad: #232621; --dot: #3d4138; --ink-mark: #e27f5a;
  }
}
:root[data-theme="dark"] {
  --paper: #1b1d1a; --ink: #ecebe3; --muted: #a3a898; --line: #3a3d36;
  --accent: #e27f5a; --teal: #58b9bd; --pad: #232621; --dot: #3d4138; --ink-mark: #e27f5a;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 16px/1.6 system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  -webkit-tap-highlight-color: transparent;
}
a { color: inherit; }
button { font: inherit; color: inherit; }
a:focus-visible, button:focus-visible, summary:focus-visible { outline: 3px solid var(--teal); outline-offset: 4px; }
.wrap { width: min(1120px, calc(100% - 48px)); margin: 0 auto; }

/* ---------- header ---------- */
.site-header {
  display: flex; align-items: center; gap: 20px;
  padding: 20px 0; border-bottom: 1px solid var(--line);
}
.brand { display: inline-flex; align-items: center; gap: 10px; font-weight: 800; text-decoration: none; white-space: nowrap; }
.crumbs { flex: 1; color: var(--muted); font-size: 15px; min-width: 0; }
.crumbs a { text-decoration: none; }
.crumbs a:hover { color: var(--accent); }
.crumbs .sep { margin: 0 8px; color: var(--line); }
.crumbs [aria-current] { color: var(--ink); }
.theme-btn {
  width: 40px; height: 40px; border-radius: 50%; border: 1px solid var(--line);
  background: transparent; display: grid; place-items: center; cursor: pointer;
}
.theme-btn:hover { border-color: var(--ink); }
.theme-btn svg { width: 20px; height: 20px; fill: none; stroke: currentColor; stroke-width: 2; stroke-linejoin: round; }
.langs { display: flex; gap: 2px; }
.langs a { padding: 5px 8px; border-radius: 999px; font-size: 13px; font-weight: 700; letter-spacing: .03em; color: var(--muted); text-decoration: none; }
.langs a:hover { color: var(--ink); }
.langs a[aria-current] { color: var(--ink); background: var(--line); }

/* ---------- intro ---------- */
.intro { padding: 34px 0 22px; }
.intro h1 {
  margin: 0; font-family: var(--display); font-weight: 800;
  font-size: clamp(40px, 6.4vw, 68px); line-height: 1.02; letter-spacing: -0.02em;
}
.lede { margin: 12px 0 0; font-size: 18px; color: var(--muted); max-width: 58ch; }

.durations { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 20px; }
.durations a {
  padding: 7px 16px; border: 1.5px solid var(--line); border-radius: 999px;
  text-decoration: none; font-size: 15px; color: var(--muted);
}
.durations a:hover { border-color: var(--ink); color: var(--ink); }
.durations a[aria-current] { background: var(--ink); border-color: var(--ink); color: var(--paper); font-weight: 600; }

.mode-switch { display: inline-flex; margin: 0 0 18px; border: 1.5px solid var(--ink); border-radius: 999px; overflow: hidden; }
.mode-switch button { border: 0; background: transparent; padding: 8px 18px; cursor: pointer; font-weight: 600; }
.mode-switch button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.stop-row { margin: 14px 0 0; min-height: 0; }
.stop-row:has([hidden]) { margin: 0; }

.challenge {
  margin: 0 0 20px; padding: 12px 16px; border-left: 4px solid var(--accent);
  background: var(--pad); font-weight: 600;
}

.actions { grid-column: 1 / -1; display: flex; flex-wrap: wrap; align-items: center; gap: 12px; margin-top: 22px; }
.btn {
  padding: 11px 22px; border-radius: 999px; border: 1.5px solid var(--ink);
  background: transparent; cursor: pointer; font-weight: 600;
}
.btn:hover { border-color: var(--accent); color: var(--accent); }
.btn.primary { background: var(--ink); color: var(--paper); }
.btn.primary:hover { background: var(--accent); border-color: var(--accent); color: #fff; }
/* ---------- article ---------- */
.prose { max-width: 70ch; margin: 56px 0 0; font-size: 17px; line-height: 1.7; }
.prose h2 { font-family: var(--display); font-weight: 800; font-size: 28px; line-height: 1.2; margin: 44px 0 10px; letter-spacing: -0.01em; }
.prose h3 { font-size: 19px; margin: 26px 0 6px; }
.prose p { margin: 0 0 14px; }
.prose ul, .prose ol { padding-left: 22px; margin: 0 0 14px; }
.prose li { margin-bottom: 6px; }
.prose a { color: var(--accent); }
.prose table { width: 100%; border-collapse: collapse; font-size: 16px; margin: 0 0 16px; }
.prose th, .prose td { border-bottom: 1px solid var(--line); padding: 9px 12px 9px 0; text-align: left; vertical-align: top; }
.prose th { border-bottom: 2px solid var(--ink); font-weight: 700; }
.prose td:first-child { font-weight: 700; white-space: nowrap; }
.faq details { border-bottom: 1px solid var(--line); padding: 12px 0; }
.faq summary { cursor: pointer; font-weight: 600; }
.faq-answer { padding: 8px 0 0; color: var(--muted); }

/* ---------- footer ---------- */
.site-footer { margin-top: 64px; padding: 22px 0 40px; border-top: 1px solid var(--line); color: var(--muted); font-size: 15px; }
.site-footer nav { display: flex; flex-wrap: wrap; gap: 6px 22px; }
.site-footer a { text-decoration: none; color: var(--ink); }
.site-footer a:hover { color: var(--accent); }
.site-footer a[aria-current] { color: var(--muted); }
.site-footer .footer-site { margin-top: 10px; padding-top: 10px; border-top: 1px solid var(--line); }
.site-footer p { margin: 10px 0 0; }

.toolbar { display: flex; flex-wrap: wrap; align-items: center; gap: 10px 14px; margin: 18px 0 0; }
.toolbar .label { color: var(--muted); font-size: 15px; }
.seg { display: inline-flex; border: 1.5px solid var(--ink); border-radius: 999px; overflow: hidden; }
.seg button { border: 0; background: transparent; padding: 7px 14px; cursor: pointer; font-weight: 600; font-variant-numeric: tabular-nums; }
.seg button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }


/* ---------- small screens (shared) ---------- */
@media (max-width: 760px) {
  .wrap { width: calc(100% - 32px); }
  .site-header { gap: 12px; padding: 14px 0; }
  .crumbs { display: none; }
  .brand { flex: 1; }
  .intro { padding: 24px 0 16px; }
  .lede { font-size: 16px; }
  .durations { flex-wrap: nowrap; overflow-x: auto; margin: 0 -16px 14px; padding: 2px 16px 6px; scrollbar-width: none; }
  .durations::-webkit-scrollbar { display: none; }
  .durations a { white-space: nowrap; flex: none; }
  .prose { font-size: 16px; margin-top: 40px; }
  .prose h2 { font-size: 23px; }
  .prose table { display: block; overflow-x: auto; }
}

/* ---------- reversi ---------- */
.rv-game { --felt: #2f7d55; --felt-edge: #1f5a3c; --grid: rgba(0, 0, 0, .28); --black: #1d1f1c; --white: #f6f3ea; max-width: 560px; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .rv-game { --felt: #24633f; --felt-edge: #17432a; } }
:root[data-theme="dark"] .rv-game { --felt: #24633f; --felt-edge: #17432a; }
.rv-score { display: flex; gap: 10px; margin: 0 0 12px; }
.rv-count {
  flex: 1; display: grid; grid-template-columns: auto auto 1fr; align-items: center; gap: 10px; padding: 8px 14px;
  border: 1.5px solid var(--line); border-radius: 14px; background: var(--pad);
}
.rv-count.is-turn { border-color: var(--ink); box-shadow: inset 0 0 0 1.5px var(--ink); }
.rv-count b { font: 800 26px/1 var(--display); font-variant-numeric: tabular-nums; }
.rv-count small { color: var(--muted); font-size: 14px; text-align: right; }
.rv-disc { display: block; width: 24px; height: 24px; border-radius: 50%; }
.rv-disc.is-black { background: var(--black); }
.rv-disc.is-white { background: var(--white); box-shadow: inset 0 0 0 1.5px #999; }
.rv-board {
  display: grid; grid-template-columns: repeat(8, 1fr); gap: 0; padding: 6px; border-radius: 16px;
  background: var(--felt); border: 3px solid var(--felt-edge); touch-action: manipulation;
}
.rv-sq {
  position: relative; display: block; aspect-ratio: 1; padding: 11%; border: 0; border-radius: 0; margin: 0;
  background: transparent; box-shadow: inset -1px -1px 0 var(--grid), inset 1px 1px 0 rgba(255, 255, 255, .06); cursor: default; color: inherit;
}
.rv-sq:not(:disabled) { cursor: pointer; }
@media (hover: hover) { .rv-sq:not(:disabled):hover { background: rgba(255, 255, 255, .14); } }
.rv-sq:focus-visible { outline: 3px solid #ffd34d; outline-offset: -3px; }
.rv-sq i { display: block; width: 100%; height: 100%; border-radius: 50%; }
.rv-sq.is-black i { background: radial-gradient(circle at 35% 30%, #55594f, var(--black) 60%); box-shadow: 0 2px 3px rgba(0, 0, 0, .35); }
.rv-sq.is-white i { background: radial-gradient(circle at 35% 30%, #fff, var(--white) 55%, #d9d4c4); box-shadow: 0 2px 3px rgba(0, 0, 0, .3); }
.rv-sq.is-legal i { width: 26%; height: 26%; margin: 37%; background: rgba(0, 0, 0, .3); }
.rv-board[data-turn="white"] .rv-sq.is-legal i { background: rgba(255, 255, 255, .45); }
.rv-sq.is-hint { background: rgba(255, 211, 77, .45); }
.rv-sq.is-last::after { content: ""; position: absolute; left: 50%; top: 50%; width: 14%; aspect-ratio: 1; margin: -7% 0 0 -7%; border-radius: 50%; background: #e0612f; }
.rv-sq.is-flip i { animation: flip .38s ease-in-out; }
@keyframes flip { 0% { transform: scaleX(1); } 50% { transform: scaleX(.05); } 100% { transform: scaleX(1); } }
.rv-board.is-over .rv-sq i { transition: opacity .3s; }
.rv-status { margin: 14px 0 0; min-height: 1.6em; font-weight: 600; }
.rv-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin: 12px 0 0; }
.rv-check { display: inline-flex; align-items: center; gap: 8px; margin-left: 4px; font-size: 15px; cursor: pointer; }
.rv-check input { width: 18px; height: 18px; accent-color: var(--accent); }
.rv-result { margin: 18px 0 0; padding: 16px 18px; border-left: 4px solid var(--ink); background: var(--pad); }
.rv-result.is-win { border-left-color: var(--teal); }
.rv-result-head { margin: 0; font: 800 26px/1.2 var(--display); }
.rv-result-sub { margin: 6px 0 12px; color: var(--muted); }
.rv-result-sub:empty { margin: 6px 0 0; }
.rv-bar { margin: 22px 0 0; padding-top: 16px; border-top: 1px solid var(--line); }
.rv-group { display: inline-flex; align-items: center; gap: 10px; }
.rv-group[hidden] { display: none; }
.rv-note { margin: 12px 0 0; color: var(--muted); font-size: 15px; }

/* ---------- diagrams in the articles ---------- */
.rv-fig { margin: 22px 0; }
.rv-fig-row { display: flex; flex-wrap: wrap; gap: 18px; }
.rv-fig-board { flex: 0 1 300px; min-width: 0; display: flex; flex-direction: column; gap: 4px; }
.rv-fig-board span { color: var(--muted); font-size: 14px; font-weight: 600; }
.rv-fig svg { display: block; width: 100%; height: auto; max-width: 300px; }
.rv-fig figcaption { margin: 8px 0 0; color: var(--muted); font-size: 15px; }
.rv-fig .bd { fill: #2f7d55; }
.rv-fig .gl { stroke: rgba(0, 0, 0, .3); stroke-width: 1; }
.rv-fig .co { fill: var(--muted); font: 600 13px system-ui, sans-serif; }
.rv-fig .dk { fill: #1d1f1c; }
.rv-fig .lt { fill: #f6f3ea; stroke: #8d8a80; stroke-width: 1; }
.rv-fig .dt { fill: rgba(0, 0, 0, .35); }
.rv-fig .nw { fill: none; stroke: #e0612f; stroke-width: 3; }
.rv-fig .tn { fill: #e0612f; }
.rv-fig .sh-c { fill: #f2c230; }
.rv-fig .sh-x { fill: #d9483b; }
.rv-fig .sh-o { fill: #f0a35e; }
.rv-fig .lb { fill: #1d1f1c; font: 800 15px system-ui, sans-serif; }

@media (max-width: 760px) {
  .rv-board { padding: 4px; border-radius: 12px; }
  .rv-count { padding: 7px 10px; gap: 8px; }
  .rv-count b { font-size: 22px; }
  .rv-bar { gap: 8px 10px; }
  .rv-bar .label { font-size: 13px; }
  .rv-bar .seg button { padding: 5px 10px; font-size: 14px; }
  .rv-fig-board { flex-basis: 100%; }
  .rv-fig-pair .rv-fig-board { flex: 1 1 140px; }
}
@media (prefers-reduced-motion: reduce) { .rv-sq.is-flip i { animation: none; } }