:root { --ink:#243431; --muted:#6f7c78; --paper:#f5f3eb; --surface:#fffdf8; --line:#d6d8d0; --teal:#4c8580; --teal-soft:#dcece8; --amber:#bd8d53; --success:#4f8b69; }
* { box-sizing:border-box; }
body { margin:0; background:var(--paper); color:var(--ink); font-family:"Hiragino Sans","Yu Gothic","Noto Sans JP",sans-serif; }
button,input { font:inherit; }
.site-shell { width:min(100%,760px); margin:0 auto; padding:42px 18px 30px; }
.hero { padding:0 8px 24px; }
.eyebrow { margin:0 0 10px; color:var(--teal); font-size:.82rem; font-weight:700; letter-spacing:.14em; }
h1 { margin:0; max-width:650px; font-size:clamp(2rem,7vw,3.5rem); line-height:1.15; letter-spacing:-.04em; }
.intro { max-width:610px; margin:18px 0 0; color:var(--muted); line-height:1.9; }
.lesson { overflow:hidden; border:1px solid rgba(36,52,49,.09); border-radius:30px; background:var(--surface); box-shadow:0 22px 60px rgba(49,65,60,.09); padding:clamp(18px,5vw,34px); }
.controls { display:grid; grid-template-columns:repeat(2,1fr); gap:12px; }
.controls label { display:grid; gap:7px; color:var(--muted); font-size:.78rem; font-weight:700; letter-spacing:.04em; }
.input-wrap { display:flex; align-items:center; gap:8px; border:1px solid var(--line); border-radius:14px; background:#fff; padding:2px 12px; }
.input-wrap input { min-width:0; width:100%; border:0; outline:0; background:transparent; color:var(--ink); padding:10px 0; font-weight:700; }
.input-wrap:focus-within { border-color:var(--teal); box-shadow:0 0 0 3px var(--teal-soft); }
.input-wrap b { color:var(--muted); font-size:.8rem; }
.message { min-height:2.8em; margin:18px 0 2px; text-align:center; color:var(--muted); font-size:.9rem; }
.geometry { display:block; width:100%; touch-action:none; user-select:none; }
.upper-zone { fill:rgba(76,133,128,.055); }
.lower-zone { fill:rgba(189,141,83,.05); }
.frame { fill:none; stroke:var(--line); stroke-width:2; }
.midline { stroke:var(--teal); stroke-width:3; }
.piece { stroke-width:2.5; }
.piece-a { fill:rgba(76,133,128,.27); stroke:var(--teal); }
.piece-b { fill:rgba(189,141,83,.27); stroke:var(--amber); }
.fixed-base { stroke:var(--muted); stroke-width:3; }
.handle { fill:var(--surface); stroke-width:3; cursor:grab; }
.handle:active { cursor:grabbing; }
.handle-a { stroke:var(--teal); }
.handle-b { stroke:var(--amber); }
.snap-halo { fill:rgba(79,139,105,.10); stroke:var(--success); stroke-width:3; }
.measure,.dimension-label,.formula { fill:var(--muted); font-size:13px; }
.dimension { stroke:var(--muted); stroke-width:1.5; }
.answer rect { fill:var(--ink); }
.answer text { fill:var(--surface); font-size:14px; font-weight:700; }
.actions { display:flex; justify-content:center; flex-wrap:wrap; gap:10px; margin-top:2px; }
.actions button { border:1px solid var(--line); border-radius:999px; background:transparent; color:var(--ink); padding:11px 18px; font-weight:700; cursor:pointer; }
.actions button.primary { border-color:var(--ink); background:var(--ink); color:var(--surface); }
.actions button:focus-visible { outline:3px solid var(--teal-soft); outline-offset:2px; }
footer { padding:24px 8px 0; text-align:center; color:var(--muted); font-size:.82rem; }
.problem-divider { padding:58px 8px 22px; }
.problem-divider span { color:var(--amber); font-size:.78rem; font-weight:800; letter-spacing:.15em; }
.problem-divider h2 { margin:8px 0 8px; font-size:clamp(1.55rem,5vw,2.25rem); letter-spacing:-.03em; }
.problem-divider p { margin:0; color:var(--muted); line-height:1.7; }
.given { display:flex; justify-content:center; flex-wrap:wrap; gap:10px; }
.given span { border:1px solid var(--line); border-radius:999px; padding:8px 14px; color:var(--muted); font-size:.82rem; }
.given b { color:var(--ink); margin-left:5px; }
.second-frame { fill:rgba(255,253,248,.7); stroke:var(--line); stroke-width:2; stroke-dasharray:6 5; }
.guide { stroke:var(--line); stroke-width:1.5; stroke-dasharray:5 5; }
.sum-piece { stroke:var(--amber); stroke-width:3; fill:rgba(210,172,85,.34); }
.bottom-piece { fill:rgba(189,141,83,.25); }
.shared-base { stroke:var(--ink); stroke-width:4; }
.line-drag circle,.edge-handle { fill:var(--surface); stroke:var(--teal); stroke-width:4; cursor:grab; }
.edge-handle { stroke:var(--amber); }
.base-five,.height-eight { fill:var(--muted); font-size:15px; font-weight:700; }
.height-eight { dominant-baseline:middle; }
.second-formula { font-size:17px; font-weight:700; }
.reason { display:grid; gap:6px; margin:4px auto 20px; max-width:440px; border-radius:18px; background:var(--teal-soft); padding:16px 18px; color:var(--muted); font-size:.86rem; text-align:center; }
.reason b { color:var(--teal); font-size:.94rem; }
.parallel-line { stroke:var(--muted); stroke-width:2; }
.third-piece { stroke-width:2.5; }
.third-a { fill:rgba(76,133,128,.25); stroke:var(--teal); }
.third-i { fill:rgba(189,141,83,.27); stroke:var(--amber); }
.cross-line { stroke:var(--ink); stroke-width:2.2; }
.bc-line { stroke:var(--muted); stroke-width:3; }
.third-handle { fill:var(--surface); stroke:var(--teal); stroke-width:4; cursor:grab; }
.third-point { fill:var(--surface); stroke:var(--amber); stroke-width:3; }
.third-e { fill:var(--surface); stroke:var(--success); stroke-width:3; }
.point-label { fill:var(--ink); font-size:14px; font-weight:800; }
.area-letter { fill:var(--ink); font-size:20px; font-weight:800; }
.e-height { stroke:var(--muted); stroke-width:1.5; stroke-dasharray:4 4; }
.third-formula { font-size:15px; }
.third-height-label { fill:var(--muted); font-size:13px; font-weight:700; writing-mode:vertical-rl; }
.hint-card { display:grid; gap:7px; margin:4px auto 14px; max-width:520px; border:1px solid rgba(189,141,83,.28); border-radius:18px; background:rgba(246,232,209,.58); padding:16px 18px; color:var(--muted); font-size:.84rem; line-height:1.65; }
.hint-card b { color:#9b6b34; font-size:.95rem; text-align:center; }
.third-controls { grid-template-columns:repeat(3,1fr); }
.square-shape { fill:rgba(76,133,128,.04); stroke:var(--teal); stroke-width:2.5; }
.extension-line { stroke:var(--muted); stroke-width:2; }
.acf-piece { fill:rgba(76,133,128,.25); stroke:var(--teal); stroke-width:2.5; }
.def-piece { fill:rgba(189,141,83,.28); stroke:var(--amber); stroke-width:2.5; }
.construction-line { stroke:var(--ink); stroke-width:2.2; }
.construction-line.secondary { stroke:var(--amber); }
.fourth-handle { fill:var(--surface); stroke:var(--success); stroke-width:4; cursor:grab; }
.fourth-formula { font-size:14px; }
@media (max-width:460px) { .site-shell{padding-top:26px}.hero{padding-bottom:18px}.lesson{border-radius:24px}.controls,.third-controls{grid-template-columns:1fr}.message{font-size:.8rem} }
@media (prefers-reduced-motion:reduce) { *,*::before,*::after{scroll-behavior:auto!important} }