:root{color-scheme:dark;--bg:#0c1628;--panel:#122039;--border:#2c4362;--fg:#f1f6ff;--muted:#b2c6e2;--accent:#7ce4d7}
*{box-sizing:border-box}html,body{margin:0;width:100%;height:100%;overflow:hidden}
body{font-family:system-ui,-apple-system,"Hiragino Kaku Gothic ProN","Yu Gothic",Meiryo,sans-serif;color:var(--fg);background:var(--bg)}
button{font:inherit;cursor:pointer;touch-action:manipulation}button:focus-visible{outline:3px solid #fff6b6;outline-offset:3px}
[hidden]{display:none!important}#app{width:100%;height:100vh;height:100dvh;display:flex}
#viewer{position:relative;min-width:0;min-height:0;flex:1;background:radial-gradient(ellipse at 48% 40%,#233d60 0%,#12243b 44%,#080f1c 100%);overflow:hidden}
#graph{display:block;width:100%;height:100%;touch-action:none;cursor:grab}#graph:active{cursor:grabbing}
#brand{pointer-events:none;position:absolute;top:0;left:0;right:64px;padding:max(20px,env(safe-area-inset-top)) 18px 0}
#brand .eyebrow{font-size:10px;font-weight:800;letter-spacing:.16em;color:#91c7de}
#brand h1{font-size:clamp(21px,4.7vw,30px);margin:5px 0 3px;letter-spacing:-.04em;line-height:1.2}
#brand .subtitle{font-size:12px;color:var(--muted);margin-top:5px;line-height:1.4}
#viewReset{width:38px;height:38px;border:1px solid #63738a;background:#132238e8;color:#e6f5ff;border-radius:12px;font-size:22px;line-height:1}
#gesture{pointer-events:none;position:absolute;bottom:13px;left:50%;transform:translateX(-50%);font-size:11px;color:#cddded;white-space:nowrap;background:#081527b8;border-radius:999px;border:1px solid #9acbd03d;padding:6px 11px}
#panel{width:350px;flex-shrink:0;padding:25px 22px;display:flex;flex-direction:column;gap:17px;overflow-y:auto;overscroll-behavior:contain;background:linear-gradient(160deg,#172944 0%,#111d33 100%);border-left:1px solid var(--border)}
#progress{display:flex;align-items:center;justify-content:space-between;gap:10px;color:#b4c9e1;font-size:12px;font-variant-numeric:tabular-nums}
#round{font-weight:800;color:var(--accent);letter-spacing:.08em}
.prompt{font-size:20px;line-height:1.45;letter-spacing:-.02em;font-weight:780;margin:0}
.note{font-size:12px;color:var(--muted);line-height:1.65;margin:0}
.actions{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.answerBtn{border:1px solid #64bfc6;background:linear-gradient(180deg,#20415a,#1a364e);color:#eaffff;border-radius:15px;min-height:60px;font-size:16px;font-weight:800;box-shadow:0 4px 12px #0003}
.answerBtn:active{background:#367183;transform:translateY(1px)}
#hintBtn{width:100%;border:1px solid #526783;background:#1b2b43;border-radius:12px;min-height:43px;color:#c5d7ed;font-size:13px;font-weight:650}
#hintBtn:active{background:#264764}#hintBtn[aria-expanded="true"]{border-color:#bd9cf1;color:#f2e4ff;background:#322a52}
#hintTools{background:#172a42;border:1px solid #4b6582;border-radius:15px;padding:12px;display:flex;flex-direction:column;gap:10px}
.hintHeader{display:flex;gap:8px;align-items:baseline;justify-content:space-between}.hintHeader strong{font-size:14px;color:#f7e3ff}.hintHeader span{font-size:11px;color:#c2d4ec}
.hintRow{display:flex;gap:12px;align-items:center}.discWrap{width:47%;max-width:174px;min-width:122px;flex-shrink:0;display:flex;justify-content:center}
#discPicker{width:100%;height:auto;aspect-ratio:1;display:block;touch-action:none;cursor:crosshair;user-select:none;border-radius:50%;outline-offset:3px}
#discPicker:focus-visible{outline:2px solid #ffe59c}#discHit{cursor:crosshair}
.hintSide{flex:1;min-width:0;display:flex;flex-direction:column;gap:9px;justify-content:center}
.hintSide label{display:flex;justify-content:space-between;gap:6px;align-items:center;font-size:13px;font-weight:750}
.hintSide output{font-variant-numeric:tabular-nums;color:#ffdbe9;font-size:12px}
#radiusSlider{width:100%;accent-color:#d7a5f5;min-height:29px;touch-action:pan-y;cursor:pointer}
#centerReset{border:1px solid #7285a2;background:#20344b;color:#e6f2ff;border-radius:10px;padding:9px 6px;font-size:12px;font-weight:700;min-height:37px}
.hintNote{font-size:11px;line-height:1.5;color:#b9cae2;margin:0}
#panel.hintExpanded #progress{position:sticky;top:0;z-index:4;background:#172943;padding:4px 0}
#panel.hintExpanded:not(.answered) #choicePanel{position:sticky;top:23px;z-index:3;background:#172943;padding:5px 0;border-radius:8px}
#panel.answered.hintExpanded{overflow-y:auto}#panel.answered.hintExpanded #resultPanel{flex:none;overflow:visible}
#resultPanel{display:flex;flex-direction:column;gap:11px}
#panel.answered{overflow:hidden}#panel.answered #resultPanel{min-height:0;flex:1;overflow-y:auto;overscroll-behavior:contain;padding-right:3px}#panel.answered #nextBtn{flex-shrink:0}
#status{font-size:22px;font-weight:800;letter-spacing:-.025em}
#status.right{color:#8ef0c7}#status.wrong{color:#ffb3ab}
#verdict{color:#dbe8f9;font-size:13px;font-weight:650;margin-top:-5px}
.mathCard{border:1px solid #405674;background:#101b30;border-radius:14px;padding:12px 12px 13px;display:flex;flex-direction:column;gap:6px}
.mathLabel{font-size:11px;font-weight:700;letter-spacing:.05em;color:#acc4df}
.mathFormula{font:19px/1.55 Georgia,'Times New Roman',serif;color:#fff;overflow-wrap:anywhere;word-break:normal}
.mathFormula.hessian{font-size:16px}
.mathFormula .zb{text-decoration:overline;text-decoration-thickness:1px;text-decoration-skip-ink:none}
.mathFormula sup{font-size:.68em;vertical-align:super}
.mathFormula i{font-style:italic}
#why{font-size:12px;line-height:1.6;color:#c4d7ed;margin:0}
.legend{display:flex;flex-direction:column;gap:6px}
.legend .caption{font-size:11px;font-weight:750;color:#d5e4f3}
.legendBar{height:12px;border:1px solid #bac4db5d;border-radius:99px;background:linear-gradient(90deg,#f04457 0%,#f9fbff 50%,#347cf8 100%)}
.legendLabels{display:flex;justify-content:space-between;gap:8px;font-size:10px;color:#b7c9e2}
#nextBtn{width:100%;min-height:52px;border:0;border-radius:13px;background:#81e5d8;color:#0b2b32;font-size:16px;font-weight:850;box-shadow:0 4px 16px #0004}
#nextBtn:active{background:#a3f9e9}
#viewerMessage{display:none;position:absolute;left:50%;top:52%;transform:translate(-50%,-50%);width:min(86%,310px);padding:15px;background:#182a41ee;border:1px solid #8296b2;border-radius:12px;text-align:center;font-size:13px;line-height:1.6;color:#fff}
#panelFoot{margin-top:auto;padding-top:6px;border-top:1px solid #334965;font-size:11px;line-height:1.55;color:#91acc8}
@media(max-width:760px){
 #app{flex-direction:column}#viewer{min-height:195px}
 #panel{width:100%;max-height:51dvh;flex-shrink:0;border-left:0;border-top:1px solid var(--border);padding:13px max(16px,env(safe-area-inset-right)) max(12px,env(safe-area-inset-bottom)) max(16px,env(safe-area-inset-left));gap:10px}
 #brand{padding:max(13px,env(safe-area-inset-top)) 14px 0}#brand h1{font-size:23px}#brand .subtitle{font-size:11px}
 #viewReset{width:35px;height:35px}
 .prompt{font-size:17px}.answerBtn{min-height:54px;font-size:15px}
 #hintBtn{min-height:36px}#gesture{bottom:9px;padding:5px 10px}
 #hintTools{padding:9px 11px;gap:6px}.hintRow{gap:11px}.discWrap{width:40%;max-width:155px;min-width:116px}.hintSide{gap:5px}
 #centerReset{min-height:34px}.hintNote{font-size:10.5px}
 #status{font-size:19px}.mathCard{padding:9px 11px;gap:3px}.mathFormula{font-size:17px}.mathFormula.hessian{font-size:15px}
 #resultPanel{gap:8px}#why{line-height:1.45}#nextBtn{min-height:47px}
 #panelFoot{display:none}
}
@media(max-width:760px) and (max-height:650px){#panel{max-height:55dvh}#brand .subtitle{display:none}#gesture{display:none}}
@media(max-height:490px) and (orientation:landscape){#app{flex-direction:row}#panel{width:min(44vw,340px);max-height:none;border-left:1px solid var(--border);border-top:0}#brand h1{font-size:21px}#panelFoot{display:none}}
@media(prefers-reduced-motion:reduce){button:active{transform:none}}

/* Main menu and informational pages */
html,body{height:100%;overflow:auto}body{min-height:100dvh}.screen{min-height:100dvh}.screen[hidden]{display:none!important}
#gameScreen{height:100dvh;min-height:0;overflow:hidden}#gameScreen #app{height:100%;}
.landing,.subpage{overflow-y:auto;background:radial-gradient(ellipse 72% 38% at 53% 7%,#24466a 0%,#132843 49%,#0a1425 100%)}
.shell{width:min(100%,770px);padding:24px 22px max(30px,env(safe-area-inset-bottom));margin:0 auto}
.topline,.pageTop{display:flex;align-items:center;justify-content:space-between;gap:14px}.topline{font-size:10px;font-weight:850;letter-spacing:.12em;color:#a5d5e1;flex-wrap:wrap}
.languageControl{display:flex;align-items:center;gap:8px;font-size:12px;letter-spacing:0;color:#d5e5ff}
select{font:inherit;font-size:13px;color:#ecf5ff;background:#162e4b;border:1px solid #53718d;border-radius:9px;padding:9px 10px;max-width:100%}
.hero{text-align:center;padding:30px 14px 21px}.hero h1{font-size:clamp(36px,8.5vw,65px);letter-spacing:-.055em;margin:10px 0 7px;line-height:1.1}.qmark{color:#7ce4d7}.hero p{max-width:580px;margin:14px auto 0;color:#cfdef2;font-size:14px;line-height:1.85}
.orb{width:124px;height:90px;margin:0 auto;display:grid;place-items:center;perspective:400px}.orb div{width:95px;height:62px;border-radius:50%;transform:rotateX(63deg) rotate(-23deg);border:5px solid #87f3ec;box-shadow:0 0 0 8px #65dce411,0 0 25px #3cc7f477,0 0 0 16px #65dce408;position:relative}.orb div:after{content:'';position:absolute;left:19px;top:12px;width:31px;height:25px;border:3px solid #d0b7ff;border-radius:50%;transform:rotate(28deg)}
.setupCard{border:1px solid #496382;background:#10223ade;border-radius:20px;padding:19px 19px 17px;box-shadow:0 20px 38px #0107114d}
.sectionTitle{font-size:13px;font-weight:780;color:#e3efff;margin:0 0 11px}.sectionTitle:not(:first-child){margin-top:22px}
.modeGrid,.levelGrid{display:grid;gap:9px}.modeGrid{grid-template-columns:1fr 1fr}.levelGrid{grid-template-columns:repeat(3,1fr)}.pick{position:relative;cursor:pointer}.pick input{position:absolute;opacity:0;pointer-events:none}.radioPanel{display:flex;flex-direction:column;justify-content:center;gap:6px;min-height:68px;padding:11px 12px;border:1px solid #4b6885;background:#142b45;border-radius:12px}.radioPanel strong{font-size:13px;line-height:1.35}.radioPanel small{font-size:11px;color:#a9c4e0;line-height:1.4}.pick input:checked+.radioPanel{border-color:#7ce4d7;background:#1b4659;box-shadow:0 0 0 1px #7ce4d7 inset}.pick input:focus-visible+.radioPanel{outline:3px solid #fff0ab;outline-offset:2px}
.levelGrid .radioPanel{min-height:49px;text-align:center;align-items:center}.setupFooter{display:flex;justify-content:space-between;gap:12px;align-items:center;margin-top:22px}.smallMuted{font-size:12px;color:#b5cbe5;line-height:1.6}.primary{border:0;border-radius:12px;background:#81e5d8;color:#092d34;font-weight:850;padding:14px 21px;min-height:50px;box-shadow:0 4px 16px #0004}.primary:hover{background:#a0f6ed}
.homeLinks{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-top:14px}.tileBtn{background:#142841;border:1px solid #456482;border-radius:13px;color:#e9f4ff;font-weight:740;min-height:63px;padding:12px 8px}.tileBtn:hover,.secondary:hover{background:#25415c}.countChip{display:inline-block;margin-left:4px;font-size:11px;color:#93e8cf}.homeFooter{font-size:10px;color:#9ab3ce;text-align:center;margin-top:22px}
.pageTop{margin-bottom:19px;justify-content:flex-start}.pageTop h2{font-size:clamp(21px,5vw,30px);margin:0}.backBtn,.secondary{border:1px solid #54718c;background:#1b324d;color:#f0f8ff;border-radius:10px;padding:10px 12px;font-weight:730;min-height:41px}
.filterRow{display:flex;gap:11px;margin-top:19px}.filterRow label{display:flex;flex-direction:column;gap:8px;flex:1;color:#c1d6ea;font-size:12px}.progressMeta{font-size:13px;font-weight:800;color:#94e8dd;margin:17px 0}.galleryGrid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}.galleryCard{background:#13243a;border:1px solid #3f5774;color:#fff;min-height:114px;border-radius:13px;padding:9px;display:flex;flex-direction:column;gap:8px;align-items:center;justify-content:center;overflow:hidden}.galleryCard.unknown{opacity:.73;background:#111d30}.galleryCard .num{font-size:10px;color:#afc7e5}.galleryCard .formulaMini{font:15px/1.35 Georgia,serif;text-align:center;overflow-wrap:anywhere;max-width:100%}.galleryCard .lock{font-size:27px;color:#8a9fb8}.galleryCard:not(.unknown):hover{background:#26425f;border-color:#7ce4d7}
.rules h3{font-size:16px;margin:27px 0 8px;color:#9fece1}.rules p,.subpage p{font-size:14px;line-height:1.8;color:#d2e2f3}.rules .legendBar{margin-top:10px}.formulaPlain{overflow-x:auto;border-radius:11px;background:#0f2036;border:1px solid #425876;padding:13px;font:15px/1.5 Georgia,serif;white-space:nowrap}
.saveBox{background:#13253b;border:1px solid #48617f;border-radius:15px;padding:19px;display:flex;flex-direction:column;gap:15px}.uploadLabel{font-size:13px;font-weight:750;color:#cce4fd}.saveBox input[type=file]{max-width:100%;font-size:12px;color:#e1ecff}.saveBox #importOptions{border-top:1px solid #53657b;padding-top:11px}.saveBox .actions button{border:1px solid #88a5c3;background:#29425e;color:#fff;border-radius:9px;padding:11px;font-weight:700}
.viewButtons{position:absolute;top:max(18px,env(safe-area-inset-top));right:16px;display:flex;gap:8px}.viewButtons button{width:38px;height:38px;border:1px solid #63738a;background:#132238e8;color:#e6f5ff;border-radius:12px;font-size:22px;line-height:1}.viewButtons #gameHome{font-size:20px}
#brand{right:104px}#galleryBack{width:100%;margin-top:3px}
.mathFormula{overflow-wrap:anywhere}#approxNote{font-size:11px;color:#bcd0ec}.legend .caption{line-height:1.45}
@media(max-width:760px){.shell{padding:17px 15px max(27px,env(safe-area-inset-bottom))}.hero{padding:13px 0 18px}.orb{width:98px;height:62px}.orb div{transform:rotateX(63deg) rotate(-23deg) scale(.77)}.hero p{font-size:12px;margin-top:10px;line-height:1.75}.setupCard{padding:15px 12px}.modeGrid{grid-template-columns:1fr 1fr}.radioPanel{padding:10px 9px;min-height:70px}.radioPanel strong{font-size:12px}.radioPanel small{font-size:10px}.homeLinks{grid-template-columns:repeat(3,1fr);gap:7px}.tileBtn{min-height:65px;font-size:11px;padding:8px 5px}.galleryGrid{gap:8px}.galleryCard{min-height:100px}.filterRow{gap:7px}.pageTop{flex-wrap:wrap}.viewButtons{top:max(13px,env(safe-area-inset-top));right:12px}.viewButtons button{width:35px;height:35px}#brand{right:98px}#panel.answered{overflow-y:auto}#panel.answered #resultPanel{overflow:visible;flex:none}#panel.answered #nextBtn{position:sticky;bottom:0;z-index:2}#panel.answered.hintExpanded #resultPanel{overflow:visible}}
@media(max-width:380px){.hero h1{font-size:36px}.topline{font-size:9px}.radioPanel strong{font-size:11px}.levelGrid .radioPanel{min-height:47px;padding:7px 4px}}

/* Discreet one-tap zoom for smartphones (pinch is also supported). */
.zoomControls{position:absolute;z-index:4;bottom:11px;left:14px;display:flex;gap:6px}
.zoomControls button{width:36px;height:36px;display:grid;place-items:center;border:1px solid #708aa6;background:#132238e8;color:#e5f8ff;border-radius:11px;font-size:22px;font-weight:500;line-height:1;touch-action:manipulation}
.zoomControls button:active{background:#31516f}
@media(max-width:760px){.zoomControls{left:11px;bottom:8px}.zoomControls button{width:32px;height:32px}}

/* v2.2: optical zoom controls. Position above gesture label, with a live magnification indicator. */
.zoomControls{bottom:46px;left:14px;display:flex;align-items:center;gap:6px;z-index:5}
.zoomControls button{width:40px;height:40px;font-size:24px;cursor:pointer}
#zoomLevel{display:grid;place-items:center;min-width:48px;font-size:12px;font-weight:750;font-variant-numeric:tabular-nums;color:#e0f2ff;background:#15263ce5;border-radius:8px;padding:9px 4px}
@media(max-width:760px){.zoomControls{left:11px;bottom:43px}.zoomControls button{width:38px;height:38px}}

/* Counterexample-circle control in the answer panel */
#witnessBtn{align-self:flex-start;max-width:100%;white-space:normal;text-align:left;font-size:12px;line-height:1.35}

/* v2.4: independent orange counterexample and purple exploratory circles. */
#witnessBtn{width:100%;align-self:stretch;border-color:#cf8757;color:#ffe6d1;background:#3c2a2d;text-align:center;padding:10px 12px;min-height:43px;font-size:12px;font-weight:760;line-height:1.4}
#witnessBtn:hover,#witnessBtn.witnessActive{background:#573a32;border-color:#ff9b53;color:#fff1db}
#witnessBtn.witnessActive{box-shadow:inset 3px 0 #ff9651}
.witnessKey{font-size:11px;color:#ffc29e;line-height:1.5;margin:0}
#discWitness,#discWitnessCenter{pointer-events:none}

#answerBanner{display:flex;flex-direction:column;gap:6px;border-left:3px solid #8fcde2;padding:3px 9px 4px;background:#24334b85;border-radius:4px}
#answerBanner #verdict{margin-top:0}
#answerBanner #status{font-size:18px}