.s50 { --s50-accent: var(--math); padding-top: 42px; padding-bottom: 100px; }
.s50 button { cursor: pointer; }
.s50 button:disabled { cursor: not-allowed; opacity: .45; }
.s50 [hidden] { display: none !important; }
.s50-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; }
.s50-back { display: inline-block; margin-bottom: 34px; color: var(--ink-soft); font: 11px var(--mono); text-decoration: none; }
.s50-back:hover { color: var(--math); }
.s50-overline { margin: 0; color: var(--math); font: 10px/1.5 var(--mono); letter-spacing: .1em; text-transform: uppercase; }
.s50-hero { display: flex; align-items: center; justify-content: space-between; gap: 20px; border-bottom: 1px solid var(--line); padding-bottom: 38px; }
.s50-hero h1 { max-width: 820px; margin: 10px 0 16px; font: 500 clamp(43px,6vw,76px)/.96 var(--display); letter-spacing: -.045em; }
.s50-hero p:last-child { max-width: 650px; margin: 0; color: var(--ink-soft); font-size: 14px; }
.s50-hero-mark { flex: none; display: grid; place-items: center; position: relative; width: 140px; height: 140px; border: 1px solid var(--line); border-radius: 50%; color: var(--math); font: 500 92px/.8 var(--display); }
.s50-hero-mark span { position: absolute; right: -12px; bottom: 4px; display: grid; place-items: center; width: 44px; height: 44px; border-radius: 50%; background: var(--signal); color: #171914; font: 13px var(--mono); }
.s50-status { display: grid; grid-template-columns: minmax(220px, 1fr) repeat(3, minmax(90px, 130px)); gap: 12px; margin: 24px 0 12px; }
.s50-meter, .s50-stat { min-width: 0; padding: 17px 19px; border: 1px solid var(--line); border-radius: 14px; background: var(--paper-raised); }
.s50-meter-copy, .s50-stat { display: flex; flex-direction: column; }
.s50-meter-copy strong, .s50-stat strong { font: 500 25px/1 var(--display); }
.s50-meter-copy span, .s50-stat span { margin-top: 6px; color: var(--ink-soft); font: 9px/1.4 var(--mono); text-transform: uppercase; }
.s50-track { height: 5px; margin-top: 14px; overflow: hidden; border-radius: 6px; background: var(--paper-deep); }
.s50-track span { display: block; height: 100%; border-radius: inherit; background: var(--math); transition: width .2s; }
.s50-save-copy, .s50-save-error { margin: 0 0 24px; color: var(--ink-soft); font: 10px/1.5 var(--mono); }
.s50-save-error { color: var(--error); }
.s50-shell { display: grid; grid-template-columns: minmax(225px, 280px) minmax(0, 1fr); gap: clamp(22px,4vw,54px); align-items: start; }
.s50-rail { position: sticky; top: calc(var(--topbar-height) + 24px); padding: 20px; border: 1px solid var(--line); border-radius: var(--radius-lg); background: var(--paper-raised); }
.s50-rail-head { display: flex; justify-content: space-between; align-items: baseline; }
.s50-rail-head strong { font: 500 19px var(--display); }
.s50-rail-head span { color: var(--ink-soft); font: 9px var(--mono); }
.s50-filters { display: flex; gap: 3px; margin: 17px 0; padding: 3px; border: 1px solid var(--line); border-radius: 9px; }
.s50-filters button { flex: 1; padding: 6px 3px; border: 0; border-radius: 6px; background: transparent; color: var(--ink-soft); font: 9px var(--mono); }
.s50-filters button.active { background: var(--ink); color: var(--paper); }
.s50-number-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 5px; }
.s50-num { position: relative; display: grid; place-items: center; aspect-ratio: 1; border: 1px solid var(--line); border-radius: 8px; background: var(--paper); color: var(--ink-soft); font: 10px var(--mono); }
.s50-num:hover { border-color: var(--math); color: var(--math); }
.s50-num.active { border-color: var(--math); background: var(--math); color: var(--paper); font-weight: 700; }
.s50-num.correct:not(.active)::after, .s50-num.incorrect:not(.active)::after, .s50-num.revealed:not(.active)::after, .s50-num.started:not(.active)::after { content: ""; position: absolute; bottom: 3px; width: 4px; height: 4px; border-radius: 50%; background: var(--success); }
.s50-num.incorrect:not(.active)::after { background: var(--error); }
.s50-num.revealed:not(.active)::after { background: var(--math); }
.s50-num.started:not(.active)::after { background: var(--ink-soft); }
.s50-legend { display: grid; grid-template-columns: 1fr 1fr; gap: 7px; margin-top: 19px; color: var(--ink-soft); font: 9px/1.3 var(--mono); }
.s50-legend span { display: flex; align-items: center; gap: 5px; }
.s50-legend i { width: 6px; height: 6px; border-radius: 50%; background: var(--ink-soft); }
.s50-legend i.correct { background: var(--success); }.s50-legend i.incorrect { background: var(--error); }.s50-legend i.revealed { background: var(--math); }
.s50-main { min-width: 0; }
.s50-card { overflow: hidden; border: 1px solid var(--line); border-radius: var(--radius-lg); background: var(--paper-raised); box-shadow: var(--shadow); scroll-margin-top: calc(var(--topbar-height) + 20px); }
.s50-card-top { display: flex; justify-content: space-between; gap: 12px; padding: 31px 34px 24px; border-bottom: 1px solid var(--line); }
.s50-card h2 { margin: 5px 0 3px; font: 500 clamp(27px,3vw,36px)/1.05 var(--display); }
.s50-difficulty { color: var(--ink-soft); font: 10px var(--mono); }
.s50-bookmark { align-self: start; display: flex; align-items: center; gap: 6px; padding: 5px; border: 0; background: none; color: var(--ink-soft); font-size: 23px; line-height: 1; }
.s50-bookmark.active { color: var(--math); }.s50-bookmark span { font: 10px var(--mono); }
.s50-source-stem { padding: 22px 34px; border-bottom: 1px solid var(--line); background: var(--paper-deep); }
.s50-source-stem > span { color: var(--ink-soft); font: 9px var(--mono); text-transform: uppercase; letter-spacing: .08em; }
.s50-source-stem p { margin: 9px 0 0; font-size: 13px; white-space: pre-line; }.s50-source-stem ol { margin: 9px 0 0; padding-left: 23px; font-size: 12px; }.s50-source-stem li { margin: 4px 0; }
.s50-part-tabs { display: flex; flex-wrap: wrap; gap: 5px; padding: 15px 34px 0; }
.s50-part-tabs button { display: inline-flex; align-items: center; gap: 6px; padding: 6px 9px; border: 1px solid var(--line); border-radius: 7px; background: transparent; color: var(--ink-soft); font: 10px var(--mono); }
.s50-part-tabs button.active { border-color: var(--math); background: var(--math-soft); color: var(--math); }
.s50-part-tabs span { width: 5px; height: 5px; border-radius: 50%; background: var(--ink-soft); }.s50-part-tabs span.correct { background: var(--success); }.s50-part-tabs span.incorrect { background: var(--error); }
.s50-question { padding: 29px 34px 8px; }.s50-prompt-label { margin: 0 0 10px; color: var(--math); font: 10px var(--mono); text-transform: uppercase; letter-spacing: .05em; }
.s50-prompt { font: 500 clamp(18px,2.4vw,24px)/1.5 var(--display); overflow-wrap: anywhere; }
.s50-graph-hint { margin: 13px 0 0; padding: 10px 12px; border-left: 3px solid var(--math); background: var(--math-soft); color: var(--ink-soft); font-size: 11px; }
.s50-graph-hint button { padding: 0; border: 0; background: none; color: var(--math); font-size: inherit; text-decoration: underline; }
.s50-figure { margin: 18px 0 0; }.s50-figure img { max-width: 100%; height: auto; border-radius: 8px; }
.s50-choices { display: grid; gap: 9px; margin: 12px 34px 0; padding: 0; border: 0; }
.s50-choice { display: flex; align-items: flex-start; gap: 14px; padding: 13px 15px; border: 1px solid var(--line); border-radius: 10px; background: var(--paper); cursor: pointer; font-size: 13px; line-height: 1.5; }
.s50-choice:hover, .s50-choice:has(input:checked) { border-color: var(--math); background: var(--math-soft); }
.s50-choice.is-answer { border-color: var(--success); }.s50-choice.is-wrong { border-color: var(--error); }
.s50-choice input { flex: none; margin: 4px 0 0; accent-color: var(--math); }.s50-choice-letter { flex: none; display: grid; place-items: center; width: 21px; height: 21px; border: 1px solid var(--line-strong); border-radius: 5px; font: 10px var(--mono); }
.s50-actions { display: flex; flex-wrap: wrap; gap: 8px; padding: 22px 34px; }.s50-actions button, .s50-footer-actions button, .s50-footer-actions a { min-height: 36px; padding: 8px 13px; border: 1px solid var(--line); border-radius: 8px; background: transparent; color: var(--ink); font: 10px var(--mono); text-decoration: none; }
.s50-actions .s50-primary { border-color: var(--math); background: var(--math); color: var(--paper); }.s50-actions .s50-text { border-color: transparent; color: var(--math); }
.s50-actions button:hover, .s50-footer-actions button:hover, .s50-footer-actions a:hover { border-color: var(--math); }
.s50-help, .s50-feedback, .s50-solution { margin: 0 34px 16px; padding: 16px 19px; border-radius: 10px; background: var(--math-soft); font-size: 12px; }
.s50-help strong, .s50-feedback strong { display: block; margin-bottom: 4px; font: 600 11px var(--mono); }.s50-help p, .s50-feedback p, .s50-solution p { margin: 0; }
.s50-feedback.correct { border-left: 3px solid var(--success); }.s50-feedback.incorrect { border-left: 3px solid var(--error); }.s50-feedback.revealed { border-left: 3px solid var(--math); }
.s50-solution { background: var(--paper-deep); }.s50-solution > p:last-of-type { white-space: pre-line; }.s50-solution .s50-overline { margin-bottom: 9px; }
.s50-notes { display: block; padding: 15px 34px 31px; border-top: 1px solid var(--line); }.s50-notes span { display: block; margin-bottom: 8px; color: var(--ink-soft); font: 10px var(--mono); }
.s50-notes textarea { display: block; width: 100%; min-height: 70px; resize: vertical; padding: 11px 13px; border: 1px solid var(--line); border-radius: 9px; background: var(--paper); color: var(--ink); font: 12px/1.5 var(--sans); }
.s50-next { display: flex; align-items: center; justify-content: space-between; gap: 8px; padding: 20px 0; }.s50-next button { padding: 8px 0; border: 0; background: none; color: var(--math); font: 11px var(--mono); }.s50-next span { color: var(--ink-soft); font: 9px var(--mono); }
.s50-footer-actions { display: flex; flex-wrap: wrap; gap: 7px; border-top: 1px solid var(--line); padding-top: 20px; }.s50-footer-actions a { margin-left: auto; color: var(--math); }
.s50-lab { margin-top: 86px; padding: 32px; border: 1px solid var(--line); border-radius: var(--radius-lg); background: var(--paper-raised); scroll-margin-top: calc(var(--topbar-height) + 20px); }
.s50-section-head { display: flex; align-items: start; justify-content: space-between; gap: 20px; }.s50-section-head h2 { margin: 8px 0 0; font: 500 clamp(29px,4vw,43px)/1.1 var(--display); }
.s50-supplement { flex: none; padding: 6px 9px; border: 1px solid var(--line); border-radius: 100px; color: var(--ink-soft); font: 9px var(--mono); }.s50-lab > p { color: var(--ink-soft); font-size: 12px; }
.s50-lab-layout { display: grid; grid-template-columns: minmax(0,1.45fr) minmax(220px,.8fr); gap: 24px; margin-top: 22px; }.s50-chart-wrap { min-width: 0; padding: 10px; border: 1px solid var(--line); border-radius: 12px; background: var(--paper); }
.s50-plot { width: 100%; height: auto; max-height: 430px; }.s50-plot-bg { fill: var(--paper); }.s50-grid-line { fill: none; stroke: var(--line); stroke-width: .75; }.s50-axis { fill: none; stroke: var(--ink-soft); stroke-width: 1.5; }.s50-plot text { fill: var(--ink-soft); font: 10px var(--mono); }.s50-curve { fill: none; stroke: var(--math); stroke-width: 3.5; stroke-linecap: round; }.s50-endpoint { fill: var(--signal); stroke: var(--math); stroke-width: 2; }
.s50-chart-caption { padding: 8px 12px; color: var(--ink-soft); font: 11px/1.6 var(--mono); }.s50-chart-caption strong { color: var(--ink); font-weight: 500; }
.s50-window-note { margin: 0; padding: 0 12px 9px; color: var(--ink-soft); font: 10px/1.5 var(--mono); }
.s50-controls { display: grid; gap: 12px; align-content: start; }.s50-slider { display: grid; gap: 6px; }.s50-slider span { display: flex; justify-content: space-between; color: var(--ink-soft); font: 10px var(--mono); }.s50-slider output { color: var(--ink); }.s50-slider input { width: 100%; accent-color: var(--math); }
.s50-flip { display: flex; justify-content: space-between; padding: 10px 12px; border: 1px solid var(--line); border-radius: 8px; background: var(--paper); color: var(--ink); font: 11px var(--mono); }.s50-control-note { margin: 0; color: var(--ink-soft); font-size: 11px; }.s50-presets { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; }.s50-presets span { width: 100%; color: var(--ink-soft); font: 9px var(--mono); text-transform: uppercase; }.s50-presets button { padding: 6px 9px; border: 1px solid var(--line); border-radius: 7px; background: transparent; color: var(--math); font: 10px var(--mono); }
@media (max-width: 1000px) { .s50-shell { grid-template-columns: 1fr; }.s50-rail { position: static; }.s50-number-grid { grid-template-columns: repeat(10,1fr); }.s50-legend { display: flex; flex-wrap: wrap; gap: 12px; } }
@media (max-width: 700px) { .s50 { padding-top: 25px; }.s50-hero-mark { display: none; }.s50-status { grid-template-columns: repeat(3,1fr); }.s50-meter { grid-column: 1/-1; }.s50-stat { padding: 13px 10px; }.s50-stat strong { font-size: 21px; }.s50-stat span { font-size: 8px; }.s50-number-grid { grid-template-columns: repeat(10,1fr); }.s50-num { font-size: 9px; }.s50-card-top, .s50-source-stem, .s50-question, .s50-notes { padding-left: 20px; padding-right: 20px; }.s50-part-tabs { padding-left: 20px; padding-right: 20px; }.s50-choices { margin-left: 20px; margin-right: 20px; }.s50-actions { padding-left: 20px; padding-right: 20px; }.s50-help, .s50-feedback, .s50-solution { margin-left: 20px; margin-right: 20px; }.s50-lab { padding: 20px; }.s50-lab-layout { grid-template-columns: 1fr; }.s50-section-head { flex-direction: column; }.s50-footer-actions a { margin-left: 0; } }
@media (max-width: 430px) { .s50-number-grid { grid-template-columns: repeat(5,1fr); }.s50-rail { padding: 15px; }.s50-next span { display: none; }.s50-hero h1 { font-size: 43px; } }