.switchback-page { max-width: 1120px; }
.intro-switchback { padding: 3.8rem 0 2.7rem; }
.eyebrow { font-size: .65rem; color: var(--accent); letter-spacing: .07em; }
.prototype { color: var(--muted); margin-left: 1.2rem; letter-spacing: 0; }
.intro-switchback h1 { font-size: clamp(2rem, 4.7vw, 3.65rem); letter-spacing: -.07em; margin: .8rem 0 1rem; line-height: 1.1; }
.intro-switchback h1 > span:first-child { color: var(--muted); }
.title-mark { display: inline-block; margin-left: .35em; color: var(--accent); }
.intro-switchback > p:last-child { font-size: .85rem; max-width: 71ch; }
.instrument { display: grid; grid-template-columns: minmax(0, 1.4fr) minmax(310px, 1fr); grid-template-rows: min-content 1fr; column-gap: 3rem; align-items: start; }
.board-section { grid-column: 1; grid-row: 1; }
.board-guide { grid-column: 1; grid-row: 2; min-width: 0; }
.workbench { grid-column: 2; grid-row: 1 / span 2; min-width: 0; }
.board-heading { display: flex; align-items: center; justify-content: space-between; gap: 1rem; padding: .1rem 0 .8rem; border-bottom: 1px solid var(--line); }
.board-heading h2 { font-size: .85rem; color: var(--heading); letter-spacing: -.025em; }
.board-heading .eyebrow { margin-right: .5rem; }
.board-heading > span { font-size: .6rem; color: var(--muted); }
.board-wrap { width: 100%; margin-top: .8rem; }
#board { display: block; width: 100%; height: auto; overflow: visible; }
#board:focus-visible { outline: 2px solid var(--focus); outline-offset: 2px; border-radius: 3px; }
.keyboard-help { font-size: .62rem; color: var(--muted); margin: -.3rem 0 .8rem; }
.visually-hidden { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; border: 0; }
.tile { fill: var(--surface); stroke: var(--line); stroke-width: 1.2; }
.tile-wall { fill: var(--bg); stroke: var(--line); stroke-width: 1; }
.hatch { stroke: var(--line); stroke-width: .75; }
.grid-label { font-family: inherit; font-size: 13px; fill: var(--muted); text-anchor: middle; dominant-baseline: central; }
.switch-symbol { fill: #d9a05d; }
.switch-glyph { fill: var(--bg); font-size: 23px; font-family: inherit; text-anchor: middle; dominant-baseline: central; }
.edit-outline { fill: none; stroke: #d9a05d; stroke-width: 2; stroke-dasharray: 5 4; }
.exit-outline { fill: none; stroke: var(--accent); stroke-width: 2; }
.exit-label { fill: var(--accent); font-family: inherit; font-size: 25px; text-anchor: middle; dominant-baseline: central; }
.start-marker { fill: none; stroke: var(--muted); stroke-width: 2; }
.route-line { fill: none; stroke: var(--accent); stroke-width: 4; stroke-linecap: round; stroke-linejoin: round; opacity: .6; }
.route-dot { fill: var(--accent); opacity: .7; }
.revisited-tile { fill: none; stroke: var(--accent); stroke-width: 2.5; }
.player-disc { fill: var(--heading); stroke: var(--bg); stroke-width: 3; }
.player-arrow { fill: var(--bg); }
.legend { display: flex; justify-content: center; flex-wrap: wrap; gap: .4rem 1.5rem; margin: .8rem 0 1.1rem; font-size: .65rem; color: var(--muted); }
.legend > span { display: inline-flex; gap: .45rem; align-items: center; }
.legend i { font-style: normal; font-size: 1.1rem; line-height: 1; }
.legend-player { color: var(--heading); }.legend-switch { color: #d9a05d; }.legend-exit { color: var(--accent); }
.board-note { display: flex; align-items: baseline; gap: .75rem; padding: .9rem 0; border-top: 1px solid var(--line); color: var(--muted); font-size: .72rem; }
.tiny-arrow { color: var(--accent); font-size: 1.3rem; }
.board-text { margin-top: .5rem; font-size: .67rem; color: var(--muted); }
.board-text summary { padding: .5rem 0; text-decoration: underline; text-underline-offset: .25em; }
.board-text pre { line-height: 1.9; font-size: .8rem; color: var(--heading); }
.section-label { display: flex; justify-content: space-between; align-items: center; gap: .7rem; margin-bottom: 1rem; }
.section-label h2 { font-size: .8rem; color: var(--heading); letter-spacing: -.025em; }
.section-label > span { font-size: .65rem; color: var(--muted); white-space: nowrap; }
.section-label strong { color: var(--heading); font-weight: 500; }
.state-strip { display: flex; align-items: center; gap: 1.6rem; background: var(--surface); padding: .85rem 1rem; border-left: 2px solid var(--accent); }
.state-strip > div { display: flex; flex-direction: column; gap: .15rem; }
.state-label { color: var(--muted); font-size: .58rem; }
.state-strip strong { color: var(--heading); font-size: .9rem; font-weight: 500; white-space: nowrap; }
.coordinate { margin-left: auto; color: var(--muted); font-size: .7rem; }
#mobile-moves { display: none; }
.rule-copy { font-size: .7rem; margin: .9rem 0; color: var(--muted); }
.move-buttons { display: grid; grid-template-columns: 1fr 1fr; gap: .65rem; }
.switchback-page button { cursor: pointer; }
.action-button { display: flex; align-items: center; gap: .7rem; justify-content: center; min-height: 70px; border: 1px solid var(--accent); background: transparent; border-radius: 4px; text-align: left; color: var(--heading); font-size: .75rem; padding: .65rem; transition: background .12s; }
.action-button:not(:disabled):hover { background: var(--surface); }
.action-icon { font-size: 1.65rem; line-height: 1; color: var(--accent); }
.action-copy { display: flex; flex-direction: column; }
.action-target { color: var(--accent); font-size: .62rem; }
.action-button small { display: block; color: var(--muted); font-size: .56rem; margin-top: .2rem; }
.switchback-page button:disabled { cursor: default; opacity: .5; }
.action-button:disabled { border-color: var(--line); }
.small-controls { display: flex; justify-content: space-between; gap: .75rem; margin-top: .65rem; }
.small-controls button, .text-button { min-height: 36px; padding: .2rem 0; background: none; border: 0; color: var(--muted); font-size: .65rem; }
.small-controls button:hover, .text-button:hover { color: var(--accent); }
kbd { font: inherit; font-size: .55rem; margin-left: .3rem; opacity: .7; }
.message { margin: .6rem 0 1.1rem; min-height: 3.5em; font-size: .72rem; color: var(--heading); }
.message[data-kind="won"] { color: var(--accent); }
.solution-panel { border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.hints { padding: .1rem 0 .8rem; font-size: .72rem; }
.hints > .eyebrow { margin-bottom: .5rem; }
.hint-actions { display: flex; justify-content: space-between; gap: 1rem; margin-top: .6rem; }
.hint-actions .text-button { text-align: left; }
.hint-actions #next-hint { color: var(--accent); }
.success-panel { border-left: 2px solid var(--accent); padding: .2rem 0 .3rem .8rem; margin-bottom: 1rem; }
.success-panel > p { font-size: .7rem; color: var(--heading); margin-bottom: .6rem; }
.followup-buttons, .experiment-actions { display: flex; flex-wrap: wrap; gap: .5rem; }
.followup-buttons button, .experiment-actions button { min-height: 42px; border: 1px solid var(--line); border-radius: 3px; background: var(--surface); color: var(--heading); padding: .5rem .7rem; font-size: .65rem; }
.followup-buttons button:hover, .experiment-actions button:not(:disabled):hover { border-color: var(--accent); }
.challenge-status { border-left: 2px solid var(--accent); padding-left: .6rem; margin: .3rem 0 1rem; font-size: .62rem; color: var(--accent); }
.reveal-button { width: 100%; display: flex; justify-content: space-between; gap: .5rem; align-items: center; min-height: 56px; background: none; border: 0; padding: .6rem 0; color: var(--accent); font-size: .73rem; text-align: left; }
#walkthrough { padding: 1rem 0; }
#walkthrough .section-label { margin-bottom: .4rem; }
#walkthrough .section-label h2 { font-size: .7rem; }
.reveal-step { font-size: .65rem; color: var(--muted); margin-bottom: .7rem; }
.replay-buttons { display: flex; gap: .5rem; }
.replay-buttons button { min-height: 42px; padding: .5rem .7rem; border: 1px solid var(--line); border-radius: 3px; color: var(--heading); background: var(--surface); font-size: .65rem; }
.replay-buttons button:last-child { margin-left: auto; }
.step-explanation { margin-top: .8rem; font-size: .7rem; min-height: 3.5em; }
.revisit { margin-top: .8rem; border-left: 2px solid var(--accent); padding-left: .8rem; font-size: .65rem; }
.revisit strong { display: block; color: var(--accent); font-weight: 500; margin-bottom: .35rem; }
.revisit > span { display: block; color: var(--muted); }
.edit-panel { padding-top: 1.5rem; }
.edit-panel > summary { display: flex; justify-content: space-between; gap: 1rem; padding: .8rem 0; font-size: .73rem; color: var(--heading); }
.edit-panel > summary::before { content: '+'; color: var(--accent); margin-right: .2rem; }
.edit-panel[open] > summary::before { content: '−'; }
.edit-panel > summary > span { margin-left: auto; font-size: .6rem; color: var(--muted); }
.experiment-body { border-top: 1px solid var(--line); padding-top: 1rem; }
.experiment-body > p:not(.eyebrow) { font-size: .7rem; color: var(--muted); }
.experiment-body .prediction-status { font-size: .64rem !important; margin: .7rem 0; }
.experiment-actions { margin: .7rem 0 1rem; }
.experiment-proof { font-size: .63rem; color: var(--muted); margin-top: .7rem; }
.experiment-proof > summary { padding: .4rem 0; text-decoration: underline; text-underline-offset: .2em; }
.experiment-proof > p { padding: .4rem 0; }
.edit-panel h2 { font-size: .9rem; color: var(--heading); margin: .4rem 0 .75rem; letter-spacing: -.03em; }
.edit-panel > p:not(.eyebrow) { font-size: .7rem; color: var(--muted); }
.edit-panel strong { color: var(--heading); font-weight: 500; }
.tile-choice { display: flex; margin: 1rem 0; border: 1px solid var(--line); border-radius: 4px; padding: 3px; }
.tile-choice button { flex: 1; background: transparent; border: 1px solid transparent; border-radius: 2px; min-height: 40px; font-size: .72rem; color: var(--muted); }
.tile-choice button[aria-pressed="true"] { background: var(--surface); color: var(--heading); border-color: var(--line); }
.solver-result { display: flex; gap: .6rem; align-items: baseline; font-size: .75rem; }
.solver-result strong { color: var(--accent); }
.solver-result p { font-size: .65rem; color: var(--muted); margin-top: .2rem; }
.result-dot { width: 6px; height: 6px; border-radius: 100%; background: var(--accent); flex: 0 0 auto; }
.solver-result[data-solvable="false"] strong { color: #d9a05d; }
.solver-result[data-solvable="false"] .result-dot { background: #d9a05d; }
.edit-panel .edit-note { font-size: .59rem !important; margin-top: .8rem; }
.under-the-hood { margin-top: 3rem; border-top: 1px solid var(--line); }
.under-the-hood summary { justify-content: space-between; font-size: .75rem; color: var(--heading); padding: 1.3rem 0; }
.under-the-hood summary span { color: var(--accent); }
.explanation { max-width: 78ch; font-size: .75rem; padding-bottom: 1rem; }
.explanation p + p { margin-top: .8rem; }
.explanation strong { color: var(--heading); font-weight: 500; }
.switchback-page footer { margin-top: 1.5rem; padding-bottom: 2rem; font-size: .62rem; }
.notice { padding: 1rem; border: 1px solid var(--line); margin-bottom: 1rem; }
:root[data-theme="light"] .switch-symbol { fill: #9c642b; }
:root[data-theme="light"] .edit-outline { stroke: #9c642b; }
:root[data-theme="light"] .legend-switch, :root[data-theme="light"] .solver-result[data-solvable="false"] strong { color: #875018; }
@media (max-width: 900px) {
  .instrument { column-gap: 1.8rem; grid-template-columns: minmax(0, 1.25fr) minmax(280px, 1fr); }
  .state-strip { gap: .85rem; padding: .8rem; }
  .legend { gap: .3rem .8rem; }
  .prototype { display: none; }
}
@media (max-width: 700px) {
  :root { scroll-padding-block: .75rem; }
  .switchback-page { width: calc(100% - 2rem); max-width: 500px; padding-bottom: max(1rem, env(safe-area-inset-bottom)); }
  .topbar { padding-top: .6rem; }
  .intro-switchback { padding: .8rem 0 1.1rem; }
  .intro-switchback > .eyebrow { display: none; }
  .intro-switchback h1 { font-size: clamp(1.7rem, 7.5vw, 2.7rem); margin: .3rem 0 .7rem; }
  .intro-switchback > p:last-child { font-size: .76rem; }
  .desktop-break { display: none; }
  .eyebrow { font-size: .57rem; }
  .instrument { display: flex; flex-direction: column; gap: .8rem; }
  .board-section, .workbench, .board-guide { width: 100%; }
  .board-wrap { max-width: min(100%, max(15rem, calc(100svh - 17rem))); margin: .5rem auto 0; }
  .legend { margin: .4rem 0 0; }
  /* Controls stay in the document: help and results grow below the maze. */
  .play-panel { padding: 0; }
  .play-panel > .section-label, .play-panel > .rule-copy { display: none; }
  .state-strip { padding: .5rem .6rem; margin-bottom: .5rem; gap: 1.4rem; }
  .state-strip > div { flex-direction: row; align-items: baseline; gap: .4rem; }
  .state-strip strong { font-size: .78rem; }
  .state-label { font-size: .6rem; }
  .coordinate { font-size: .6rem; white-space: nowrap; }
  #mobile-moves { display: inline; }
  .move-buttons { gap: .7rem; }
  .action-button { min-height: 60px; font-size: .8rem; }
  .action-target { font-size: .65rem; }
  .action-button small, .small-controls kbd { display: none; }
  .small-controls { margin-top: .2rem; }
  .small-controls button, .text-button { min-height: 44px; font-size: .72rem; }
  .small-controls button { min-width: 44px; }
  .message { font-size: .72rem; margin: .2rem 0 .7rem; min-height: 3em; line-height: 1.5; }
  .reveal-button { min-height: 44px; font-size: .75rem; }
  .hints { font-size: .73rem; padding-bottom: .7rem; }
  .hint-actions { margin-top: .3rem; }
  .hint-actions .text-button { min-height: 44px; font-size: .68rem; }
  .success-panel { margin: .5rem 0 .8rem; }
  .success-panel > p { font-size: .72rem; }
  .followup-buttons button { min-height: 44px; font-size: .7rem; }
  .challenge-status { margin: .3rem 0 .6rem; font-size: .68rem; }
  .edit-panel { padding-top: .7rem; }
  .edit-panel > summary { min-height: 44px; }
  .tile-choice button, .experiment-actions button { min-height: 44px; }
  .board-guide { padding-top: .6rem; }
  .board-note { padding: .6rem 0; }
  .board-text { margin-top: 0; }
  .board-text summary { min-height: 44px; }
  .under-the-hood { margin-top: 2rem; }
  .switchback-page footer > span { display: none; }
  [data-revealing="true"] .play-panel > .move-buttons,
  [data-revealing="true"] .play-panel > .small-controls,
  [data-revealing="true"] .play-panel > .message { display: none; }
  #walkthrough { padding: .4rem 0; }
  #walkthrough .section-label { margin-bottom: 0; }
  #walkthrough .section-label .text-button { min-height: 44px; }
  .replay-buttons button { min-height: 44px; min-width: 44px; }
  .step-explanation { min-height: 3em; font-size: .73rem; margin-top: .6rem; }
  .revisit { margin-top: .5rem; font-size: .7rem; }
  .revisit strong { margin-bottom: .2rem; }
}
@media (max-width: 360px) {
  .board-heading h2 { font-size: .72rem; }
  .board-heading > span { font-size: .5rem; }
  .state-strip { gap: .6rem; padding: .5rem; }
  .state-strip > div { gap: .25rem; }
  .state-strip strong { font-size: .7rem; }
  .state-label, .coordinate { font-size: .55rem; }
}
@media (min-width: 701px) and (max-width: 1100px) and (max-height: 540px) {
  :root { scroll-padding-block: .5rem; }
  .board-wrap { max-width: calc(100svh - 5rem); margin-inline: auto; }
  .small-controls button, .text-button, .replay-buttons button { min-height: 44px; min-width: 44px; }
}