:root{--proof-a:#327ca1;--proof-b:#bc7825;--proof-c:#3b8a68;--proof-d:#a85e73}
:root[data-theme="dark"]{--proof-a:#78b7d5;--proof-b:#e0ad60;--proof-c:#83c5a0;--proof-d:#d492a7}
#formulaPage{max-width:1600px;margin:0 auto;background:var(--surface);min-height:calc(100dvh - 68px);padding:var(--space-xl)}
.formula-page-head{display:flex;align-items:center;justify-content:space-between;gap:var(--space-lg);margin-bottom:var(--space-xl)}
.formula-page-head h1{font-size:27px;margin:0}
.formula-page-head>button{min-height:40px;padding:var(--space-sm) var(--space-md);font-size:14px;background:var(--raised);border-radius:var(--radius)}
.formula-shell{display:grid;grid-template-columns:252px minmax(0,1fr);gap:var(--space-xl)}
.formula-library{min-width:0;padding-right:var(--space-xl);border-right:1px solid var(--line)}
.formula-search{display:flex;align-items:center;gap:var(--space-md);padding:var(--space-md);background:var(--raised);border-radius:var(--radius);color:var(--muted)}
.formula-search input{width:100%;min-width:0;font-size:14px;background:transparent;border:0;color:var(--ink)}
.formula-course{display:flex;flex-direction:column;gap:var(--space-xs);margin-top:var(--space-lg);font-size:12px;color:var(--muted)}
.formula-course select{min-height:40px;padding:var(--space-sm);background:var(--surface);color:var(--ink);border:1px solid var(--line);border-radius:var(--radius);font:inherit;font-size:14px}
.formula-filter-row{display:flex;gap:var(--space-xs);margin:var(--space-lg) 0}
.formula-filter-row button{min-height:36px;padding:var(--space-sm) var(--space-md);font-size:12px;border-radius:var(--radius);background:var(--raised)}
.formula-filter-row button.active{background:var(--ink);color:var(--surface)}
.formula-count{font-size:12px;color:var(--muted);margin:var(--space-md) 0}
.formula-chapter-filter{display:flex;gap:var(--space-sm);align-items:center;font-size:12px;background:var(--raised);padding:var(--space-sm);border-radius:var(--radius)}
.formula-chapter-filter button{margin-left:auto;min-width:28px;font-size:22px}
#formulaList{max-height:calc(100dvh - 390px);overflow-y:auto;scrollbar-width:thin;min-height:200px}
.formula-group summary{display:flex;gap:var(--space-sm);align-items:center;cursor:pointer;min-height:40px;font-size:13px;font-weight:550}
.formula-group summary span{margin-left:auto;color:var(--muted);font-size:12px;font-weight:400}
.formula-list-item{width:100%;text-align:left;display:flex;align-items:center;gap:var(--space-sm);padding:var(--space-sm);min-height:44px;border-radius:var(--radius);font-size:13px;line-height:1.35}
.formula-list-item.selected,.formula-list-item:hover{background:var(--raised);color:var(--ink)}
.formula-list-item small{margin-left:auto;color:var(--muted);font-size:10px;white-space:nowrap}
.formula-source-links{display:flex;flex-direction:column;gap:var(--space-sm);margin-top:var(--space-xl);font-size:12px}
.formula-content{min-width:0;padding-bottom:var(--space-2xl)}
.formula-title-row{display:flex;align-items:flex-start;justify-content:space-between;gap:var(--space-lg)}
.formula-title-row h2{margin:0;font-size:25px;line-height:1.2;letter-spacing:-.7px}
.exam-label{display:block;max-width:225px;padding:var(--space-xs) var(--space-sm);background:var(--pill);color:var(--accent);font-size:11px;line-height:1.4;border-radius:3px}
.exam-label.learn{background:var(--raised);color:var(--muted)}
.formula-display{font-size:27px;overflow-x:auto;padding:var(--space-lg) var(--space-sm);margin:var(--space-md) 0;background:var(--paper);border-radius:var(--radius)}
.formula-display .katex-display{margin:var(--space-sm) 0}.formula-display .katex{font-size:1.1em}
.formula-related{display:flex;align-items:center;flex-wrap:wrap;gap:var(--space-sm);font-size:12px;color:var(--muted)}
.formula-related button{min-height:32px;padding:var(--space-xs) var(--space-sm);border-bottom:1px solid var(--line);color:var(--accent);font-size:12px}
.proof-heading{display:flex;align-items:flex-start;justify-content:space-between;gap:var(--space-xl);margin:var(--space-xl) 0 var(--space-md)}
.proof-heading h3{margin:0;font-size:16px}
.proof-heading details{font-size:12px;color:var(--muted);max-width:52%;position:relative}
.proof-heading summary{cursor:pointer;min-height:30px;list-style:none}
.proof-heading details[open]{background:var(--raised);padding:var(--space-md);border-radius:var(--radius)}
.proof-heading details p{max-width:65ch;line-height:1.5}
.proof-layout{display:grid;grid-template-columns:minmax(0,1fr) 260px;gap:var(--space-lg)}
.proof-visual{min-width:0}
.proof-graphic{min-height:290px;background:var(--paper);border-radius:var(--radius);overflow:clip}
.proof-graphic>svg{display:block;stroke:none;width:100%;height:auto;max-height:430px;min-height:290px}
.proof-graphic>svg text{font-family:var(--font-body);letter-spacing:0;stroke:none}
.proof-graphic[data-draggable]{cursor:grab;touch-action:none}
.proof-metrics{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:var(--space-sm);margin-top:var(--space-md)}
.proof-metrics>div{display:flex;align-items:baseline;justify-content:space-between;gap:var(--space-sm);font-size:11px;color:var(--muted)}
.proof-metrics strong{font-size:14px;color:var(--metric-color,var(--ink));font-weight:550;font-variant-numeric:tabular-nums}
.proof-step-panel{min-width:0;padding:var(--space-lg);background:var(--raised);border-radius:var(--radius);align-self:start}
.proof-step-count{font-size:12px;color:var(--muted)}
#proofStepBody>p{font-size:15px;line-height:1.5;margin:var(--space-md) 0}
.step-equation{font-size:16px;overflow-x:auto;max-width:100%;padding:var(--space-sm) 0}
.step-equation .katex{font-size:1.05em}.step-equation .katex-display{margin:var(--space-sm) 0}
.proof-step-buttons{display:flex;justify-content:space-between;gap:var(--space-sm);margin-top:var(--space-lg)}
.proof-step-buttons button{min-height:36px;padding:var(--space-sm);font-size:12px;border-radius:var(--radius);background:var(--surface)}
.proof-step-buttons button:disabled{background:var(--paper);color:var(--disabled-ink);cursor:not-allowed}
.proof-all-steps{font-size:12px;color:var(--muted);margin-top:var(--space-xl)}
.proof-all-steps summary{cursor:pointer;min-height:32px}
.proof-all-steps ol{padding-left:var(--space-lg)}
.proof-all-steps p{font-size:13px;line-height:1.5;color:var(--ink)}
.proof-all-steps .step-equation{font-size:13px}
.proof-controls{margin-top:var(--space-xl)}
.proof-parameters{display:flex;flex-wrap:wrap;gap:var(--space-lg) var(--space-xl)}
.proof-parameters>label{flex:1 1 180px;min-width:0;font-size:12px;color:var(--muted)}
.proof-parameters>label>span{display:flex;justify-content:space-between;gap:var(--space-sm)}
.proof-parameters output{color:var(--ink);font-variant-numeric:tabular-nums}
.proof-controls input[type=range]{display:block;width:100%;margin:var(--space-md) 0;accent-color:var(--accent);min-height:24px;cursor:pointer}
.proof-controls input:focus-visible,.formula-course select:focus-visible{outline:2px solid var(--focus);outline-offset:3px}
.proof-playback{display:flex;align-items:center;gap:var(--space-lg);margin-top:var(--space-md)}
.proof-playback>button{font-size:13px;min-height:40px;min-width:66px;background:var(--raised);padding:var(--space-sm) var(--space-md);border-radius:var(--radius)}
.proof-playback>button:first-child{background:var(--ink);color:var(--surface)}
.proof-playback>label{flex:1;min-width:0;display:flex;align-items:center;gap:var(--space-md);font-size:12px;color:var(--muted)}
.proof-caption{font-size:12px;color:var(--muted);max-width:85ch;line-height:1.55;margin-top:var(--space-lg)}
@media(max-width:1250px){.proof-layout{grid-template-columns:minmax(0,1fr)}.proof-step-panel{display:grid;grid-template-columns:minmax(0,1fr) auto;gap:var(--space-sm)}.proof-step-count{grid-column:1/-1}.proof-all-steps{grid-column:1/-1;margin-top:var(--space-sm)}.proof-step-buttons{align-self:start}.proof-graphic>svg{max-height:400px}.formula-shell{grid-template-columns:220px minmax(0,1fr)}}
@media(max-width:800px){#formulaPage{padding:var(--space-lg)}.formula-shell{grid-template-columns:minmax(0,1fr)}.formula-library{padding-right:0;border-right:0;border-bottom:1px solid var(--line);padding-bottom:var(--space-lg)}#formulaList{max-height:185px;min-height:100px}.formula-course{display:inline-flex;width:calc(50% - 8px)}.formula-filter-row{display:inline-flex;margin-left:var(--space-md)}.formula-source-links{flex-direction:row;flex-wrap:wrap;margin-top:var(--space-md)}.formula-title-row h2{font-size:23px}.formula-display{font-size:23px}.proof-graphic>svg{min-height:240px}.proof-graphic>svg text{font-size:23px}.proof-graphic{min-height:240px}.proof-step-panel{display:block}.proof-step-buttons{margin-top:var(--space-md)}.proof-heading{gap:var(--space-md)}.formula-page-head h1{font-size:25px}.formula-related>span{width:100%}.exam-label{max-width:140px}.proof-parameters{gap:var(--space-lg)}}
@media(prefers-reduced-motion:reduce){#formulaPage *{transition:none!important;animation:none!important;scroll-behavior:auto!important}}

@media(max-width:700px){header #searchToggle{display:none}.proof-metrics{grid-template-columns:minmax(0,1fr)}.proof-parameters>label{flex-basis:140px}}

.exam-sheet-note{font-size:13px;color:var(--muted);margin:var(--space-lg) 0}.exam-sheet{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:var(--space-lg)}.exam-sheet-card{border-bottom:1px solid var(--line);padding:var(--space-lg) 0}.exam-sheet-title{text-align:left;width:100%;font-size:16px;font-weight:550}.exam-sheet-title span{display:block;font-size:10px;font-weight:400;color:var(--muted);margin-top:var(--space-xs)}.exam-sheet-card .formula-display{font-size:20px;padding:var(--space-sm);min-height:65px;display:flex;align-items:center;justify-content:center}.sheet-proof-link{display:block;color:var(--accent);font-size:12px;min-height:36px;margin-top:var(--space-sm)}@media(max-width:1100px){.exam-sheet{grid-template-columns:minmax(0,1fr)}}

.formula-library-summary{display:none}@media(max-width:800px){.formula-library-summary{display:flex;justify-content:space-between;align-items:center;min-height:40px;font-size:14px;cursor:pointer;list-style:none}.formula-library-summary span{font-size:12px;color:var(--muted)}.formula-library-summary::after{content:'+';font-size:20px;margin-left:var(--space-md)}#formulaLibraryDisclosure[open]>.formula-library-summary::after{content:'−'}.formula-library-summary span{margin-left:auto}#formulaLibraryDisclosure[open]>.formula-library-summary{margin-bottom:var(--space-md)}.formula-shell{gap:var(--space-lg)}}

@media(max-width:800px){.proof-graphic>svg text.proof-diagram-note{display:none}}

/* Animation is the diagram. Symbolic derivation is fixed and optional. */
.proof-layout{display:flex;flex-direction:column;gap:12px}.proof-step-panel{order:2;padding:0;background:transparent;display:block}.proof-all-steps{margin:0;font-size:13px}.proof-all-steps[open]{background:var(--raised);padding:16px}.proof-all-steps ol{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 32px}.proof-all-steps li{min-width:0}.proof-all-steps .step-equation{white-space:normal;font-size:17px}.proof-graphic>svg{max-height:580px;min-height:350px}.proof-graphic>svg text{font-size:inherit}.diagram-math .katex{font-size:1em}.diagram-math .katex-html{white-space:nowrap}.proof-metrics{display:none}.proof-caption{max-width:none;font-size:13px}.proof-all-steps summary{min-height:36px;color:var(--muted)}@media(max-width:800px){.proof-all-steps ol{grid-template-columns:minmax(0,1fr)}.proof-graphic>svg{min-height:260px}.proof-graphic>svg text{font-size:inherit}}

.proof-graphic>svg{height:360px;min-height:0;max-height:420px}.proof-graphic{min-height:0}.diagram-math .katex svg{min-height:0;max-height:none;stroke:none;fill:currentColor;stroke-width:0}.proof-heading{margin-top:16px}.formula-display{padding-top:10px;padding-bottom:10px}.proof-controls{margin-top:12px}.proof-step-panel{display:block;margin-top:12px}.proof-controls+.proof-caption{margin-top:8px}@media(min-height:950px){.proof-graphic>svg{height:430px}}@media(max-width:800px){.proof-graphic>svg{height:auto;max-height:none;min-height:0}.proof-step-panel{display:block;margin-top:12px}}