:root{--ink:#334b50;--teal:#087d86;--pale:#e7f3f1;--paper:#fbfcf9;--line:#d6e0dc;--gold:#c37a31;--pink:#b36579;--blue:#4d79b6}*{box-sizing:border-box}body{margin:0;background:#f1f4f0;color:var(--ink);font:16px/1.45 system-ui,-apple-system,Segoe UI,sans-serif}button,input,select{font:inherit}button{cursor:pointer;border:1px solid #b7c9c4;background:white;color:var(--ink);border-radius:8px;padding:9px 13px}button:hover{background:#eff8f5}button:focus-visible,input:focus-visible{outline:3px solid #e3a942;outline-offset:2px}button.active,.primary{background:var(--teal);color:#fff;border-color:var(--teal)}button:disabled{opacity:.5;cursor:default}h1{font-size:29px;margin:3px 0 4px}h2{font-size:20px;margin:0 0 8px}h3{font-size:17px;margin:0 0 7px}p{margin:7px 0}main{max-width:1410px;margin:auto;padding:18px}.top{border-bottom:1px solid var(--line);padding-bottom:14px;margin-bottom:18px}.brand{font-weight:850;font-size:18px;letter-spacing:.8px;color:var(--ink);text-decoration:none}.subbrand{color:#71847f;font-size:13px;margin-left:12px}.eyebrow{text-transform:uppercase;letter-spacing:1.5px;color:var(--teal);font-size:12px;font-weight:750}.chapters,.tabs,.presets,.toolbar{display:flex;gap:7px;flex-wrap:wrap}.chapters{margin-top:13px}.chapters button{padding:8px 10px;font-size:13px}.tabs{margin:13px 0 17px}.tabs button{font-size:14px}.panel{background:var(--paper);border:1px solid var(--line);border-radius:12px;padding:18px;margin-bottom:13px}.intro{max-width:850px}.home-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:12px}.home-grid button{text-align:left;padding:14px;min-height:150px}.home-grid strong{display:block;font-size:17px}.home-grid small{color:#6d817b}.lesson-head{display:flex;justify-content:space-between;gap:15px;align-items:start}.lesson-head p{color:#627774}.layout{display:grid;grid-template-columns:minmax(0,1fr) 340px;gap:14px}.stage{padding:10px;min-width:0}.stage svg{width:100%;height:auto;aspect-ratio:800/530;display:block;touch-action:none;border-radius:9px;background:#fff}.hintline{color:#66807b;font-size:13px;padding:6px 7px}.side .panel{padding:16px}.side label{display:block;font-size:14px;font-weight:650;margin:11px 0 4px}.side input[type=range]{width:100%;accent-color:var(--teal)}.side input[type=number],.answer{border:1px solid #b8c8c3;border-radius:7px;padding:9px;width:100%;background:#fff}.side .presets button{font-size:12px;padding:7px 9px}.task{border-left:4px solid var(--teal);padding:12px;background:var(--pale);border-radius:6px}.feedback{min-height:42px;margin-top:9px;font-size:14px}.feedback.good{color:#236f4d}.feedback.bad{color:#a14949}.step{display:flex;align-items:start;gap:13px;background:#f2f7f4;padding:14px;border-radius:8px;margin-top:12px}.step-icon{width:38px;height:38px;border-radius:50%;background:var(--teal);color:#fff;display:grid;place-items:center;flex:none;font-size:20px}.step small{display:block;color:#687b75;margin-bottom:2px}.step-controls{display:flex;gap:8px;align-items:center;flex-wrap:wrap;margin-top:10px}.tag{font-size:12px;color:#5a7772;padding:4px 9px;background:#eaf2ef;border-radius:12px}.muted{color:#6d817b}.side .toolbar{margin-top:12px}.tiny{font-size:12px}.toggle{display:flex;align-items:center;gap:7px;margin:10px 0}.toggle input{accent-color:var(--teal)}.stage svg .drag{cursor:grab}.stage svg .drag:active{cursor:grabbing}.stage svg text{font-family:system-ui,sans-serif;user-select:none}.footer{text-align:center;color:#748780;font-size:12px;padding:26px}.pagecount{margin-left:auto;color:#6c817b;font-size:13px;align-self:center}@media(max-width:970px){.layout{grid-template-columns:1fr}.home-grid{grid-template-columns:repeat(2,1fr)}}@media(max-width:600px){main{padding:10px}.home-grid{grid-template-columns:1fr}.panel{padding:13px}.stage{padding:4px}.lesson-head{display:block}.subbrand{display:block;margin-left:0}.chapters{max-height:106px;overflow:auto}.tabs{flex-wrap:nowrap;overflow:auto}.tabs button{white-space:nowrap}.side .panel{padding:13px}h1{font-size:25px}}

/* Geometry classroom layout: one visible task, simple tap targets, flat playful shapes. */
:root{--ink:#263f4b;--teal:#087e88;--pale:#eaf5ee;--paper:#fffdf7;--line:#aec6bf}
body{background:#f7f5ed;color:var(--ink)}main{max-width:1300px}.top{border-bottom:2px solid #b3c8c2}.brand{font-weight:900;letter-spacing:.4px}.chapters button.active,.tabs button.active{background:#157d89;color:white;border-color:#263f4b}.chapters button,.tabs button{border:2px solid #aec6bf;border-radius:13px;font-weight:700}.panel{background:#fffdf7;border:2px solid #9cbab2;border-radius:18px;box-shadow:4px 5px 0 #e1e9dc}.lesson-head h1{font-size:28px}.lesson-head p{font-size:14px;margin:3px 0}.stage{padding:8px;align-self:start}.stage svg{background:#fffdf7;border-radius:14px}.layout{grid-template-columns:minmax(0,1fr) 330px;align-items:start}.side .panel{padding:14px}.quiz{background:#fff9e9;border-color:#d7ad61}.quiz-kicker{font-size:14px;font-weight:850;color:#a86a2b;margin-bottom:6px}.quiz h2{font-size:20px;line-height:1.28}.choice-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px;margin-top:14px}.choice-grid button{min-height:51px;border:2px solid #5b7978;background:white;border-radius:13px;font-weight:800;text-transform:capitalize}.choice-grid button:hover{background:#e8f6f1}.choice-grid button.right{background:#c9f2cf;border-color:#338558}.choice-grid button.wrong{background:#ffe1d9;border-color:#c76d61}.quiz-actions{gap:7px}.quiz-actions button{font-size:13px;padding:7px 10px}.quiz-actions .primary{background:#087e88;color:white}.feedback{min-height:31px;font-weight:650}.feedback.reveal{color:#7750a0}.settings,.solution{box-shadow:none;background:#f9fcf8}.settings summary,.solution summary{cursor:pointer;font-weight:800;list-style:none}.settings summary::-webkit-details-marker,.solution summary::-webkit-details-marker{display:none}.settings summary::after,.solution summary::after{content:'＋';float:right;color:#087e88;font-size:20px;line-height:1}.settings[open] summary::after,.solution[open] summary::after{content:'−'}.settings .presets{margin-top:15px}.settings .presets button{border:2px solid #a8c9c2}.step-icon{background:#f1bd5e;color:#263f4b;border:2px solid #a87529}.footer.site-footer{margin:28px 0 0;padding:21px 4px 9px;border-top:1px solid #c8d6cf;text-align:center;line-height:1.7;color:#68807a;font-size:13px}
@media(max-width:850px){.layout{grid-template-columns:1fr}.side{display:contents}.stage{margin-bottom:0}.quiz{margin-top:0}.settings,.solution{grid-column:1}}
@media(max-width:600px){main{padding:8px}.top{padding-bottom:6px;margin-bottom:7px}.brand{font-size:16px}.subbrand{display:none}.chapters{flex-wrap:nowrap;overflow-x:auto;max-height:none;margin-top:7px;padding-bottom:3px}.chapters button{white-space:nowrap;padding:6px 9px;font-size:12px}.lesson-head h1{font-size:21px;margin:1px 0}.lesson-head .eyebrow{font-size:10px}.lesson-head p{display:none}.tabs{margin:7px 0;gap:5px}.tabs button{padding:6px 9px;font-size:12px}.layout{gap:7px}.panel{border-radius:13px;box-shadow:2px 3px 0 #e1e9dc}.stage{padding:3px}.stage svg{aspect-ratio:800/530}.hintline{display:none}.side .panel{padding:10px}.quiz-kicker{font-size:12px;margin:0 0 3px}.quiz h2{font-size:16px;margin:0 0 6px}.choice-grid{margin-top:7px;gap:6px}.choice-grid button{min-height:42px;font-size:14px;padding:6px}.quiz-actions button{font-size:12px;padding:6px 8px}.feedback{min-height:23px;font-size:12px;margin:5px 0}.footer.site-footer{margin-top:18px;font-size:11px}}
.concept{font-size:13px;font-weight:700;line-height:1.35;color:#385b64;background:#eaf5ee;border-radius:9px;padding:7px 9px;margin-bottom:8px}.quiz h2{margin-bottom:6px}.visual-grid{gap:8px}.choice-grid button.visual-choice{position:relative;display:flex;align-items:center;justify-content:center;padding:7px;min-height:113px;overflow:hidden}.visual-choice>svg{width:100%;height:96px;display:block}.choice-letter{position:absolute;top:5px;left:6px;background:#263f4b;color:white;border-radius:50%;width:24px;height:24px;display:grid;place-items:center;font-size:12px;z-index:1}.triple-view,.target-views{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:3px;width:100%;text-align:center}.triple-view svg,.target-views svg{width:100%;height:auto;max-height:57px;display:block}.triple-view small,.target-views small{display:block;font-size:10px;line-height:1;color:#36586a;text-transform:uppercase;font-weight:800}.target-views{margin:8px 0;background:#fff;border:1px solid #b8cfca;border-radius:10px;padding:4px}.target-views svg{max-height:85px}.turn-buttons{display:flex;gap:5px;flex-wrap:wrap;margin:8px 0}.turn-buttons button{padding:6px 10px;border:2px solid #587b82;font-weight:800}.turn-buttons button.right,.turn-buttons button.active{background:#bde7de;border-color:#17856c}.hint-progress{font-size:13px;color:#bd7137;min-height:16px;letter-spacing:3px}.choice-grid button.hint-choice{outline:3px solid #f6a249;outline-offset:-5px;animation:choicePulse 1s ease-in-out infinite alternate}.hint-pulse{transform-box:fill-box;transform-origin:center;animation:hintPulse 1.15s ease-in-out infinite alternate}.view-arrow{animation:arrowBob 1.3s ease-in-out infinite alternate}@keyframes hintPulse{to{opacity:.48;transform:scale(1.14)}}@keyframes choicePulse{to{box-shadow:0 0 0 5px #ffc46a}}@keyframes arrowBob{to{transform:translateY(8px)}}
@media(max-width:600px){.concept{font-size:11px;padding:5px 7px;margin-bottom:5px}.choice-grid button.visual-choice{min-height:94px;padding:4px}.visual-choice>svg{height:79px}.triple-view svg{max-height:47px}.choice-letter{width:20px;height:20px;font-size:10px;top:3px;left:3px}.target-views svg{max-height:60px}.turn-buttons button{font-size:12px;padding:5px 8px}}
.home-grid button{display:grid;grid-template-columns:82px 1fr;column-gap:12px;align-items:center;min-height:126px}.home-grid button .chapter-art{grid-row:span 2;width:80px;height:80px;background:#f1f7f2;border:2px solid #a8c6c3;border-radius:14px}.home-grid button strong{align-self:end}.home-grid button small{align-self:start}.stage svg .hint-card text{font-size:18px;font-weight:800;fill:#30566a}.stage svg .hint-card{animation:fadeHint .45s ease-out}.stage svg .wrong-grid{animation:wrongGrid .7s ease-out}.stage svg .circle-guide text{paint-order:stroke;stroke:#fffdf7;stroke-width:5px;font-weight:800}@keyframes fadeHint{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:translateY(0)}}@keyframes wrongGrid{to{opacity:0;transform:scale(1.2)}}@media(max-width:600px){.home-grid button{min-height:96px;grid-template-columns:64px 1fr}.home-grid button .chapter-art{width:62px;height:62px}}
.home-grid{grid-template-columns:repeat(3,minmax(0,1fr));gap:18px}.home-grid button{display:flex;flex-direction:column;align-items:stretch;min-height:0;padding:10px 10px 16px;text-align:left;border:3px solid #557982;border-radius:23px;box-shadow:5px 6px 0 #d8e5db;overflow:hidden;transition:transform .18s,box-shadow .18s}.home-grid button:hover{transform:translateY(-4px);box-shadow:5px 10px 0 #d8e5db}.home-grid button .chapter-art{display:block;width:100%;height:auto;aspect-ratio:600/240;grid-row:auto;background:none;border:0;border-radius:17px}.home-grid button strong{font-size:19px;margin:10px 7px 2px}.home-grid button small{margin:0 7px;color:#416676;font-weight:700}.intro{max-width:none;display:grid;grid-template-columns:1fr minmax(270px,44%);align-items:center;gap:15px;margin-bottom:21px;padding:20px}.intro .chapter-art{grid-column:2;grid-row:1/4;width:100%;height:auto;aspect-ratio:600/240;border:0}.intro .eyebrow,.intro h1,.intro p{grid-column:1}.intro h1{font-size:clamp(32px,4vw,55px);line-height:1.03;letter-spacing:-1.6px}.intro p{font-size:18px}.intro .eyebrow{font-size:14px}@media(max-width:970px){.home-grid{grid-template-columns:repeat(2,minmax(0,1fr))}}@media(max-width:600px){.home-grid{grid-template-columns:1fr;gap:14px}.home-grid button{padding:8px 8px 14px;border-radius:20px}.home-grid button .chapter-art{width:100%;height:auto;aspect-ratio:600/240}.home-grid button strong{font-size:21px;margin:9px 8px 2px}.intro{display:block;text-align:left;padding:14px}.intro h1{font-size:34px}.intro p{font-size:14px}.intro .chapter-art{display:block;width:100%;height:auto;margin-top:10px}}
.circle-focus{filter:drop-shadow(0 0 7px #fac259);animation:circleGlow 1.8s ease-in-out infinite alternate}@keyframes circleGlow{to{filter:drop-shadow(0 0 17px #e8a34d);opacity:.77}}
@media(max-width:600px){.stage svg.mobile-guide{aspect-ratio:800/1000}}
.polygon-diagonal{stroke-dasharray:10 7;stroke:#e88954;stroke-width:3;animation:fadeHint .6s ease-out}.angle-reasoning-mark{stroke:#e68953;stroke-width:5;fill:none}
.turn-buttons button[data-turn]{font-size:31px;line-height:1;min-width:72px;min-height:51px;background:#eaf7f1;color:#235568;border-radius:13px}@media(max-width:600px){.turn-buttons button[data-turn]{font-size:29px;min-width:66px}}
.mixed-toolbox{display:grid;grid-template-columns:repeat(4,1fr);gap:6px;margin:8px 0}.mixed-toolbox button{font-size:25px;font-weight:850;padding:6px 3px;min-height:45px;border:2px solid #5c8790;border-radius:10px;background:#eaf8f4}.mixed-toolbox button:hover{background:#d9f1e9}.mixed-choice-label{font-size:12px;color:#446f78;font-weight:750;text-align:center}

.test-level{margin:8px 0}.test-level label{font-weight:800;color:#386472}.test-level input{display:block;width:100%;accent-color:#087e88;margin:7px 0}.level-tabs{display:grid;grid-template-columns:repeat(5,1fr);gap:4px}.level-tabs button{padding:5px 0;font-weight:800;border:2px solid #719aa0}.level-tabs button.active{background:#087e88;color:#fff}.fold-net{filter:drop-shadow(2px 4px 2px #a7b8ad)}
.view-teaching-controls{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:5px;margin:8px 0}.view-teaching-controls button{padding:7px 3px;min-height:42px;font-size:12px;font-weight:750}.build-actions{display:flex;flex-wrap:wrap;gap:6px}