:root {
  font-family:Inter,"Hiragino Kaku Gothic ProN","Noto Sans JP",system-ui,sans-serif;
  color:#243d36;
  background:#f6f5ef;
  font-synthesis:none;
  --green:#23634e;
  --muted:#738079;
  --line:#dedfd5;
  --orange:#a75729;
}
* {
  box-sizing:border-box;
}
body {
  margin:0;
}
button,a,summary {
  -webkit-tap-highlight-color:transparent;
}
button {
  font:inherit;
  cursor:pointer;
  color:inherit;
  border:1px solid var(--line);
  border-radius:9px;
  background:#fff;
  padding:12px 18px;
  touch-action:manipulation;
}
button:hover {
  background:#edf2e9;
}
button:focus-visible,a:focus-visible,summary:focus-visible {
  outline:3px solid #d88041;
  outline-offset:4px;
}
main {
  max-width:1180px;
  margin:auto;
  padding:0 40px;
}
.masthead {
  height:96px;
  display:flex;
  align-items:center;
  justify-content:space-between;
  border-bottom:1px solid var(--line);
}
.brand {
  text-decoration:none;
  color:inherit;
  font-weight:850;
  letter-spacing:2px;
  font-size:21px;
  display:flex;
  align-items:center;
  gap:12px;
}
.brand-icon {
  font-size:32px;
  color:var(--green);
}
.brand-sub {
  font-size:10px;
  letter-spacing:1px;
  color:var(--muted);
  font-weight:500;
  border-left:1px solid var(--line);
  padding-left:14px;
}
.edition,.eyebrow {
  font-size:10px;
  letter-spacing:2px;
  font-weight:700;
  color:var(--green);
}
.intro {
  padding:42px 0 32px;
}
.intro .eyebrow {
  letter-spacing:2px;
  font-size:12px;
}
.intro h1 {
  font-size:clamp(27px,3.4vw,40px);
  letter-spacing:.045em;
  margin:10px 0 14px;
  line-height:1.45;
}
.intro>p:last-child {
  font-size:13px;
  color:var(--muted);
  line-height:1.9;
}
.mobile-break {
  display:none;
}
.workspace {
  display:grid;
  grid-template-columns: minmax(0,1fr) minmax(0,1.05fr);
  gap:40px;
  align-items:start;
}
.game-panel {
  background:#fff;
  border:1px solid var(--line);
  border-radius:20px;
  padding:26px;
  box-shadow:0 8px 24px #29413305;
}
.game-top {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:8px;
}
.size-select {
  display:flex;
  background:#f1f2ec;
  border-radius:9px;
  padding:4px;
  gap:2px;
}
.size-select button {
  border:0;
  background:transparent;
  padding:9px 15px;
  font-size:13px;
  font-weight:700;
}
.size-select button[aria-pressed=true] {
  background:#fff;
  color:var(--green);
  box-shadow:0 2px 6px #0000000c;
}
.mode-label {
  font-size:10px;
  color:var(--muted);
}
.board-meta {
  display:flex;
  align-items:center;
  justify-content:space-between;
  margin:26px 0 16px;
  font-size:11px;
  color:var(--muted);
}
.board-meta strong {
  font-size:28px;
  font-weight:650;
  color:#243d36;
  font-variant-numeric:tabular-nums;
}
.board {
  position:relative;
  width:100%;
  aspect-ratio:1;
  background:#e6e9df;
  border:8px solid #e6e9df;
  border-radius:14px;
  --n:3;
  --gap:7px;
}
.tile {
  position:absolute;
  left:0;
  top:0;
  width:calc((100% - (var(--n) - 1)*var(--gap))/var(--n));
  height:calc((100% - (var(--n) - 1)*var(--gap))/var(--n));
  transform:translate(calc(var(--x)*(100% + var(--gap))),calc(var(--y)*(100% + var(--gap))));
  display:flex;
  align-items:center;
  justify-content:center;
  padding:0;
  font-size:clamp(24px,3vw,40px);
  font-weight:650;
  border:1px solid #deded1;
  border-bottom:3px solid #d4d9ca;
  border-radius:9px;
  background:#fdfcf7;
  color:#2e5143;
  box-shadow:0 2px 3px #203a2b06;
  transition:transform .16s ease,background .15s,border-color .15s;
  user-select:none;
}
.tile[data-movable=true] {
  background:#fff;
  border-color:#afc4ad;
}
.tile[data-movable=true]:hover {
  background:#eef5e8;
}
.tile[data-movable=false] {
  cursor:default;
}
.tile.blank {
  background:#d8dfce88;
  border:1px dashed #bdc8b4;
  box-shadow:none;
  color:#7a8d71;
  font-size:12px;
  pointer-events:none;
}
.tile.blank .blank-number {
  display:none;
}
.math-on .tile.blank .blank-number {
  display:inline;
}
.board[data-size="5"] .tile {
  font-size:clamp(21px,2.3vw,30px);
}
.board[data-size="4"] .tile {
  font-size:clamp(24px,2.6vw,34px);
}
.status {
  text-align:center;
  min-height:41px;
  padding:15px 0 8px;
  font-size:11px;
  color:var(--muted);
}
.status.clear {
  margin-top:16px;
  padding:18px 10px;
  border:2px solid #a7c497;
  border-radius:14px;
  background:#e6edde;
  color:var(--green);
  animation:clear-appear .25s ease-out;
}
#clear-title {
  display:block;
  font-size:clamp(40px,6vw,56px);
  font-weight:900;
  letter-spacing:.08em;
  line-height:1.15;
}
.status.clear #status-message {
  display:block;
  margin-top:10px;
  font-size:clamp(12px,2vw,15px);
  font-weight:650;
  line-height:1.7;
}
@keyframes clear-appear {
  from { opacity:0; transform:translateY(5px); }
  to { opacity:1; transform:translateY(0); }
}
.actions {
  display:grid;
  grid-template-columns:1.2fr 1fr;
  gap:10px;
  margin-top:10px;
}
.actions button {
  font-size:13px;
  font-weight:650;
}
.primary {
  background:var(--green);
  color:white;
  border-color:var(--green);
}
.primary:hover {
  background:#194a3a;
}
.challenge-row {
  display:flex;
  align-items:center;
  justify-content:space-between;
  border-top:1px solid #ededE5;
  margin-top:22px;
  padding-top:16px;
}
.challenge-row>span {
  font-size:11px;
  color:var(--muted);
}
.challenge-row button {
  border:0;
  padding:8px 0 8px 12px;
  font-size:12px;
  color:var(--orange);
  font-weight:700;
}
.input-hint {
  font-size:9px;
  text-align:center;
  color:#88918a;
  margin:18px 0 0;
}
.input-hint span {
  padding:0 6px;
}
.math-area {
  padding-top:7px;
}
.math-toggle-row {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:12px;
  margin-bottom:24px;
}
.math-toggle-row .eyebrow {
  font-size:9px;
  letter-spacing:1.6px;
  margin:0 0 8px;
}
.math-toggle-row h2 {
  font-size:17px;
  letter-spacing:.04em;
  margin:0;
}
.toggle {
  display:flex;
  align-items:center;
  gap:8px;
  padding:10px;
  font-size:11px;
  background:transparent;
  border:0;
  white-space:nowrap;
}
.switch {
  width:33px;
  height:20px;
  background:#c3cac0;
  border-radius:20px;
  padding:3px;
  display:inline-block;
}
.switch:before {
  content:"";
  display:block;
  width:14px;
  height:14px;
  border-radius:50%;
  background:white;
  transition:transform .2s;
}
.toggle[aria-pressed=true] .switch {
  background:var(--green);
}
.toggle[aria-pressed=true] .switch:before {
  transform:translateX(13px);
}
#toggle-state {
  font-size:9px;
  width:22px;
  font-weight:700;
}
.placeholder {
  border:1px dashed #d6dcd0;
  border-radius:16px;
  min-height:420px;
  display:flex;
  flex-direction:column;
  justify-content:center;
  align-items:center;
  text-align:center;
  padding:25px;
}
.pattern {
  display:flex;
  gap:6px;
  transform:rotate(-7deg);
  margin:20px;
}
.pattern span {
  display:grid;
  place-items:center;
  width:44px;
  height:49px;
  border-radius:7px;
  background:#e5eadc;
  color:#547355;
  font-size:19px;
  font-weight:600;
}
.pattern span:last-child {
  background:#e9dec9;
  color:#9a7b46;
}
.placeholder h3 {
  font-size:16px;
  margin:20px 0 8px;
}
.placeholder p {
  font-size:12px;
  color:var(--muted);
  line-height:2;
}
.placeholder .placeholder-note {
  font-size:10px;
  margin-top:25px;
}
.math-note {
  font-size:11px;
  line-height:1.9;
  color:var(--muted);
}
.permutation {
  display:flex;
  flex-wrap:wrap;
  gap:4px;
  margin:12px 0 18px;
}
.permutation span {
  min-width:23px;
  padding:5px 4px;
  text-align:center;
  font-size:11px;
  border-radius:4px;
  background:#e9ece3;
  font-variant-numeric:tabular-nums;
}
.permutation .blank-chip {
  background:#d4e2c7;
  border:1px dashed #87a275;
  padding:4px 3px;
}
.metrics {
  display:grid;
  grid-template-columns:1fr 1fr;
  gap:12px;
}
.metric {
  border:1px solid var(--line);
  border-radius:12px;
  padding:16px 13px;
  background:#ffffff88;
}
.metric-title {
  font-size:12px;
  font-weight:700;
}
.metric-title>span {
  font-size:9px;
  color:#8f9e8f;
  margin-right:7px;
}
.metric-value {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:8px;
  margin:16px 0 10px;
}
.metric-value>strong {
  font-size:29px;
  line-height:1.2;
  font-variant-numeric:tabular-nums;
  font-weight:600;
  white-space:nowrap;
}
.metric p {
  font-size:9px;
  color:var(--muted);
  min-height:27px;
  line-height:1.6;
  margin:0;
}
.badge {
  display:inline-flex;
  align-items:center;
  gap:5px;
  font-size:11px;
  font-weight:750;
  white-space:nowrap;
  padding:5px 8px;
  border-radius:6px;
}
.badge.even {
  background:#e1ebda;
  color:#365f36;
}
.badge.odd {
  background:#f5e4d6;
  color:#974b24;
}
.badge.even:before {
  content:"●";
  font-size:9px;
}
.badge.odd:before {
  content:"◆";
  font-size:9px;
}
.transition {
  font-size:10px;
  border-top:1px solid var(--line);
  margin-top:10px;
  padding-top:10px;
  color:#6c7f6f;
  min-height:27px;
}
.invariant {
  background:#e6edde;
  border:1px solid #d1dfc4;
  border-radius:12px;
  margin-top:13px;
  padding:18px;
}
.invariant-top {
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:10px;
}
.invariant .eyebrow {
  font-size:9px;
  letter-spacing:1.5px;
  margin:0 0 8px;
}
.invariant h3 {
  font-size:18px;
  font-weight:600;
  margin:0;
}
.invariant .badge {
  background:#fff9;
}
.invariant>p {
  font-size:12px;
  margin:12px 0;
  color:#607255;
}
.invariant-change {
  border-top:1px solid #cbd8be;
  padding-top:10px;
  font-size:12px;
  font-weight:650;
}
.goal-compare {
  display:flex;
  justify-content:center;
  align-items:center;
  gap:24px;
  margin:19px 0 7px;
}
.goal-compare>div {
  display:flex;
  align-items:center;
  gap:10px;
}
.goal-compare>div>span {
  font-size:10px;
  color:var(--muted);
}
.compare-sign {
  color:#778875;
}
.comparison-note {
  font-size:10px;
  line-height:1.8;
  text-align:center;
  color:var(--muted);
  margin:0 0 20px;
}
.comparison-note.different {
  color:var(--orange);
}
details {
  border-top:1px solid var(--line);
}
summary {
  cursor:pointer;
  font-size:12px;
  padding:16px 0;
  font-weight:650;
}
summary>span {
  float:right;
  font-size:9px;
  font-weight:400;
  color:var(--muted);
  padding-top:2px;
}
.table-scroll {
  overflow-x:auto;
}
table {
  width:100%;
  border-collapse:collapse;
  white-space:nowrap;
  font-size:10px;
  font-variant-numeric:tabular-nums;
  text-align:center;
}
th {
  font-weight:500;
  color:var(--muted);
  padding:10px 5px;
  background:#e9ece3;
}
td {
  padding:8px 5px;
  border-bottom:1px solid #e3e7dc;
}
td:last-child {
  background:#e7eddf;
}
td .badge {
  padding:3px 5px;
  font-size:9px;
}
tbody tr:last-child {
  font-weight:750;
  background:#ffffff;
}
.history-note {
  font-size:10px;
  color:var(--muted);
  line-height:1.8;
}
.explanation-body {
  font-size:12px;
  line-height:1.95;
  padding-bottom:16px;
}
.explanation-body p {
  margin:0 0 12px;
}
.proof {
  padding:13px;
  background:#e9ece3;
  border-radius:8px;
  margin:12px 0;
  font-size:11px;
}
footer {
  border-top:1px solid var(--line);
  margin:48px 0 0;
  padding:24px 0;
  display:flex;
  justify-content:space-between;
  align-items:center;
  color:#8b968b;
  font-size:10px;
}
footer>span:first-child {
  letter-spacing:2px;
  font-weight:750;
}
footer p {
  margin:0;
}
.flash {
  animation:flash .65s ease-out;
}
@keyframes flash {
  0% {
    background:#f1d5a5;
  }
  100% {
    background:transparent;
  }
}
[hidden] {
  display:none!important;
}
@media(min-width:1000px) {
  .workspace {
    gap:52px;
  }
  .game-panel {
    padding:30px;
  }
}
@media(max-width:800px) {
  main {
    padding:0 24px;
  }
  .workspace {
    gap:25px;
    grid-template-columns:1fr;
    max-width:520px;
    margin:auto;
  }
  .intro {
    text-align:center;
    padding-top:30px;
  }
  .masthead {
    height:76px;
  }
  .edition {
    font-size:8px;
  }
  .brand-sub {
    display:none;
  }
  .math-area {
    padding-top:10px;
  }
  .placeholder {
    min-height:230px;
  }
  .pattern {
    margin:10px;
  }
  .placeholder h3 {
    margin:10px 0 0;
  }
  .placeholder .placeholder-note {
    margin:8px 0;
  }
  .tile {
    font-size:38px;
  }
  .board[data-size="5"] .tile {
    font-size:27px;
  }
  .board[data-size="4"] .tile {
    font-size:32px;
  }
}
@media(max-width:430px) {
  main {
    padding:0 16px;
  }
  .brand {
    font-size:17px;
  }
  .edition {
    letter-spacing:1px;
  }
  .intro h1 {
    font-size:28px;
  }
  .mobile-break {
    display:block;
  }
  .intro>p:last-child {
    font-size:11px;
    max-width:280px;
    margin:0 auto;
  }
  .game-panel {
    padding:18px;
  }
  .size-select button {
    padding:9px 12px;
  }
  .math-toggle-row h2 {
    font-size:15px;
  }
  .math-toggle-row {
    gap:4px;
  }
  .toggle {
    gap:5px;
    padding:7px 0;
  }
  .metric {
    padding:13px 10px;
  }
  .metric-value>strong {
    font-size:25px;
  }
  .badge {
    font-size:10px;
    padding:5px 6px;
  }
  .invariant h3 {
    font-size:16px;
  }
  footer>span:last-child {
    display:none;
  }
  .goal-compare {
    gap:14px;
  }
  .board {
    --gap:5px;
    border-width:6px;
  }
  .tile {
    font-size:32px;
  }
  .board[data-size="5"] .tile {
    font-size:23px;
  }
}
@media(prefers-reduced-motion:reduce) {
  *,*:before {
    animation:none!important;
    transition:none!important;
  }
}