:root{color-scheme:dark;--bg:#101a1e;--panel:#142329;--text:#e7f1ed;--muted:#aec2c6;--line:#31454b;--mint:#86e2cc;--amber:#eeb778;--red:#ff8b8b;--font:Inter,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI","Noto Sans JP",sans-serif;--mono:ui-monospace,SFMono-Regular,Consolas,monospace;font-family:var(--font);font-size:16px;background:var(--bg);color:var(--text)}
*{box-sizing:border-box}
html{height:100%;overflow:hidden;overflow-anchor:none}
body{margin:0;height:100vh;height:100dvh;overflow:hidden;display:grid;grid-template-rows:auto minmax(0,1fr);line-height:1.5;padding:env(safe-area-inset-top) max(12px,env(safe-area-inset-right)) max(8px,env(safe-area-inset-bottom)) max(12px,env(safe-area-inset-left))}
button,a{-webkit-tap-highlight-color:transparent;touch-action:manipulation}button{font:inherit;color:inherit;cursor:pointer}button:disabled{cursor:not-allowed;opacity:.45}button:focus-visible,a:focus-visible,[tabindex]:focus-visible{outline:2px solid var(--mint);outline-offset:3px}a{color:var(--muted);text-underline-offset:4px}a:hover{color:var(--text)}[hidden]{display:none!important}
.site-header,main{width:min(1050px,100%);margin-inline:auto;min-width:0;min-height:0}
.site-header{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:12px 0;border-bottom:1px solid var(--line)}
h1{margin:0;font-size:clamp(1.125rem,2.5vw,1.7rem);font-weight:650;letter-spacing:-.035em;line-height:1.25}h1 span{color:var(--mint);white-space:nowrap}
.languages{display:flex;gap:4px;flex-shrink:0}.languages button{border:0;border-radius:5px;background:transparent;color:var(--muted);padding:8px;font-size:.875rem;min-height:44px}.languages button[aria-pressed=true]{background:#253a3d;color:var(--text)}
main{display:grid;grid-template-rows:auto minmax(0,1fr)}
.explanation-tabs{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:4px;padding:8px 0}
.explanation-tabs button{height:52px;padding:4px 8px;border:1px solid transparent;border-radius:6px;background:transparent;color:var(--muted);font-size:.9375rem;line-height:1.35;overflow-wrap:anywhere}
.explanation-tabs button[aria-selected=true]{border-color:#48645f;background:#233d37;color:var(--mint)}.explanation-tabs button:hover{color:var(--text)}
.game-panel{min-width:0;min-height:0;display:grid;grid-template-rows:minmax(0,1fr) auto;overflow:hidden}
.experiment{min-width:0;min-height:0;display:grid;grid-template-columns:minmax(0,1fr);grid-template-rows:auto auto minmax(0,1fr) auto;grid-template-areas:"settings" "play" "stage" "status";border:1px solid var(--line);border-radius:10px;overflow:hidden;background:var(--panel)}
.toolbar{display:contents}
.course-controls{grid-area:settings;display:grid;grid-template-columns:max-content minmax(0,1fr) minmax(0,1fr);gap:8px;padding:8px 12px;border-bottom:1px solid var(--line);background:#182b30}
.wall-controls{display:flex;align-items:center;gap:8px}.wall-controls>span{width:2.5rem;flex:none;font-size:.875rem;color:var(--muted)}
.wall-count{display:flex;gap:2px;border:1px solid #486064;border-radius:6px;padding:2px}.wall-count button{background:none;border:0;border-radius:3px;width:44px;min-height:44px;padding:0}.wall-count button[aria-pressed=true]{color:var(--bg);background:var(--mint);font-weight:700}
.button{display:inline-flex;justify-content:center;align-items:center;gap:8px;height:48px;min-width:0;padding:8px 12px;border-radius:6px;border:1px solid #4c6565;font-size:.9375rem;font-weight:550;white-space:nowrap;background:#253a3e;position:relative;line-height:1.4}
.button:hover:not(:disabled){filter:brightness(1.14)}.button>[aria-hidden=true]:not(.spinner){width:1rem;flex:none;text-align:center}.primary{background:var(--mint);color:#102922;border-color:var(--mint)}.answer-action{color:#f2d5aa;border-color:#827056;background:#38342b}.quiet{background:none}.button.quiet.active{border-color:var(--mint);color:var(--mint);background:#29483f}
.play-controls{grid-area:play;display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px;padding:8px 12px}
.answer-action[aria-pressed=true]{border-color:var(--amber);box-shadow:inset 0 0 0 1px var(--amber)}
.stage{grid-area:stage;position:relative;isolation:isolate;min-width:0;min-height:0;display:grid;grid-template-rows:minmax(0,1fr) 36px;overflow:hidden;border-top:1px solid var(--line)}
.stage-top{position:absolute;top:10px;left:14px;right:14px;display:flex;justify-content:flex-end;pointer-events:none}.answer-badge{font-size:.875rem;color:var(--amber)}
/* All drags in the canvas belong to the game, including drags between handles. */
#course{width:100%;height:100%;min-width:0;min-height:0;display:block;overflow:hidden;user-select:none;-webkit-user-select:none;touch-action:none}
#grid line{stroke:#263a40;stroke-width:1;opacity:.75}.wall-fill{fill:#694c31;stroke:#eeb778;stroke-width:1.4}.rail{fill:none;stroke:var(--mint);stroke-width:3;stroke-linecap:round;stroke-linejoin:round;pointer-events:none}.rail.invalid{stroke:var(--red)}.rail.answer{stroke:#f4d8a4}
.control-polygon{fill:none;stroke:#90aaae;stroke-width:1.3;stroke-dasharray:4 7;opacity:.4;pointer-events:none}.marker-dot{fill:var(--text)}.goal-flag{fill:#dcebe5;stroke:#dcebe5;stroke-width:1.4}
.handle{outline:none;cursor:ns-resize;touch-action:none}.handle .hit{fill:transparent}.handle .halo{fill:#142329;stroke:#86e2cc;stroke-width:1;opacity:.85}.handle .core{fill:var(--mint)}.handle .handle-arrow{stroke:var(--mint);stroke-width:1.8;fill:none;opacity:0}.handle:hover .handle-arrow,.handle.selected .handle-arrow,.handle:focus-visible .handle-arrow{opacity:1}.handle.selected .halo,.handle:focus-visible .halo{stroke-width:2.5;fill:#33564d}.handle.locked{pointer-events:none}.handle.locked .halo{opacity:.28}.handle.locked .core{opacity:.35}
#ball,#answer-ball,#markers,#collision{pointer-events:none}.ball-body{fill:#f5f8e9;stroke:#101a1e;stroke-width:1}#answer-ball .ball-body{fill:var(--amber)}#collision circle{fill:#29242a;stroke:var(--red);stroke-width:1.8}#collision path{fill:none;stroke:var(--red);stroke-width:2}
.point-tools-slot{flex:none;min-width:80px;min-height:36px}.point-tools{display:flex;gap:4px;border-radius:5px}.point-tools button{background:#20353a;border:1px solid #4c6565;color:var(--mint);font-size:1.1rem;width:36px;height:36px;padding:0;border-radius:4px;touch-action:none;user-select:none;-webkit-user-select:none}.point-tools button:hover{background:#2a4547}
.score-strip{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px;align-items:center;padding:0 12px 4px;font-size:.875rem}.score-strip>div{display:flex;justify-content:center;align-items:baseline;gap:10px}.score-strip>div>span{color:var(--muted)}.score-strip strong{font-family:var(--mono);font-size:1.25rem;font-weight:450;white-space:nowrap;font-variant-numeric:tabular-nums}.score-strip small{font-family:var(--font);font-size:.875rem;font-weight:400;color:var(--muted)}.score-strip.concealed{visibility:hidden}
.stage-footer{grid-area:status;display:flex;align-items:center;gap:10px;border-top:1px solid var(--line);padding:4px 10px;color:var(--muted);font-size:.875rem;height:52px;line-height:1.4}.stage-footer>span{min-width:0}
.score-strip.comparing{grid-template-columns:repeat(3,minmax(0,1fr))}.score-strip.comparing .player-score>span{color:var(--mint)}#answer-score>span{color:var(--amber)}
.solve-message{font-size:.875rem;color:var(--muted);margin:4px;max-height:3em;overflow:auto}.solve-message:empty{display:none}.spinner{position:absolute;right:5px;top:5px;width:12px;height:12px;border:1.5px solid #837a6b;border-top-color:var(--amber);border-radius:50%;animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}
.layout-mode #markers{pointer-events:auto}.movable{cursor:grab;touch-action:none;outline:none}.movable:active{cursor:grabbing}.layout-hit{fill:transparent;stroke:none}.placement-area{fill:#86e2cc;fill-opacity:.025;stroke:#608d83;stroke-width:1;stroke-dasharray:5 7;pointer-events:none}.movable.selected .wall-fill,.movable:focus-visible .wall-fill{stroke:#f6e8c7;stroke-width:3}.movable.selected .goal-flag,.movable:focus-visible .goal-flag{stroke:var(--mint);fill:var(--mint);stroke-width:3}
/* Only the reading panels scroll; the header and tab bar stay in place. */
.reading-panel{min-width:0;min-height:0;overflow:auto;overscroll-behavior:contain;touch-action:auto;-webkit-overflow-scrolling:touch;padding:12px 8px 32px;scroll-padding-block:16px}
.help-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px}.help-grid p,.math-content p{color:var(--muted);font-size:1rem;line-height:1.8;margin:0 0 14px}.help-grid .help-note{font-size:.9375rem;border-left:2px solid #49635c;padding-left:12px;line-height:1.8}
.math-content .localized-copy{max-width:850px;margin-inline:auto}.equation{font-size:1rem;line-height:1.5;color:#d2e8e0;background:#1c3036;border-radius:6px;padding:17px 20px;margin:16px 0;overflow-x:auto}.equation .katex-display{margin:.3em 0}.equation .katex-display>.katex{white-space:nowrap}
.math-section+.math-section{margin-top:32px}.reading-panel h2{font-size:1.125rem;line-height:1.5;font-weight:600;margin:0 0 16px;color:var(--text)}.math-content p{line-height:1.9}.math-content p .katex{font-size:1.08em}.math-content .citation{font-size:.875em;color:var(--mint);margin-inline:.15em;white-space:nowrap}
.basics-section,.mathematics-section,.site-note{max-width:850px;margin-inline:auto}.mathematics-section{margin-top:32px;border-top:1px solid var(--line);padding-top:24px}.math-intro{margin-bottom:24px!important}.site-note{margin-top:32px;border-top:1px solid var(--line);padding-top:16px}.site-note p{font-size:.875rem;margin-bottom:6px}
.references{border-top:1px solid var(--line);margin-top:32px;padding-top:24px}.references ol{padding-left:1.7em;margin:0}.references li{color:var(--muted);font-size:.9375rem;line-height:1.8;margin:0 0 14px;overflow-wrap:anywhere;scroll-margin-top:16px}.references a{color:#bdded3}.localized-copy{min-width:0}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
/* A single toolbar row leaves more height for the course on desktop. */
@media(min-width:960px) and (min-height:501px){
 .site-header,main{width:min(1280px,100%)}.site-header{padding:6px 0}
 .explanation-tabs{padding:6px 0}.explanation-tabs button{height:44px}
 .experiment{grid-template-columns:minmax(0,1.35fr) minmax(0,1fr);grid-template-rows:auto minmax(0,1fr) auto;grid-template-areas:"settings play" "stage stage" "status status"}
 .course-controls{border-bottom:0}.play-controls{align-items:center;background:#182b30}
}
@media(max-width:700px){
 .site-header{padding:6px 0}.site-header h1 span{display:block}.languages{gap:0}.languages button{padding:6px}
 .explanation-tabs{gap:2px;padding:5px 0}.explanation-tabs button{font-size:.875rem;padding:3px}
 .course-controls{padding:6px;gap:5px}.wall-controls{gap:4px}.wall-controls>span{width:2.3rem}.wall-count button{width:34px}.wall-count{gap:1px}
 .button{padding:6px;gap:4px;font-size:.875rem}.play-controls{padding:6px;gap:6px}
 .stage-footer{padding:4px 10px}.help-grid{grid-template-columns:1fr;gap:16px}.score-strip{gap:6px;padding-inline:6px}.score-strip>div{gap:6px}.rail{stroke-width:4}.equation{padding:14px 10px;font-size:.9rem}
 .score-strip.comparing>div{gap:0;flex-direction:column;align-items:center;line-height:1.1}.score-strip.comparing strong{font-size:1rem}.score-strip.comparing small{font-size:.75rem}
 .stage{grid-template-rows:minmax(0,1fr) 42px}
}
@media(max-width:400px){.button>[aria-hidden=true]:not(.spinner){display:none}.wall-count button{width:30px}.course-controls{gap:4px}.course-controls .quiet{padding-inline:4px}.site-header h1{font-size:1.05rem}.languages button{font-size:.8125rem;padding:6px}.score-strip strong{font-size:1.1rem}}
/* Landscape phones put the controls beside the course, preserving canvas height. */
@media(max-height:500px) and (min-width:520px){
 body{padding-bottom:max(4px,env(safe-area-inset-bottom))}.site-header{padding:0;gap:8px}.site-header h1{font-size:1.125rem}.site-header h1 span{display:inline}.languages button{padding-block:4px}
 .explanation-tabs{padding:3px 0}.explanation-tabs button{height:44px;font-size:.875rem;padding:2px}
 .experiment{grid-template-columns:178px minmax(0,1fr);grid-template-rows:auto auto minmax(0,1fr) 44px;grid-template-areas:"settings stage" "play stage" ". stage" "status status";gap:0}
 .course-controls{grid-template-columns:repeat(2,minmax(0,1fr));padding:4px;gap:4px;border-bottom:0;background:none}.wall-controls{grid-column:1/-1;justify-content:center;gap:4px}.wall-controls>span{width:2.3rem}.wall-count{flex:1;min-width:0}.wall-count button{width:0;flex:1}
 .button{height:44px;font-size:.875rem;padding:4px}.button>[aria-hidden=true]:not(.spinner){display:none}.play-controls{padding:4px;gap:4px}
 .stage{grid-template-rows:minmax(0,1fr) 42px;border-top:0;border-left:1px solid var(--line)}.stage-footer{height:44px;font-size:.875rem;line-height:1.25;padding:2px 8px}.score-strip strong{font-size:1.05rem}.score-strip{font-size:.875rem}.score-strip small{font-size:.8125rem}.stage-top{top:5px}
}
@media(prefers-reduced-motion:reduce){.spinner{animation:none}}