:root{color-scheme:light;--ink:#18372e;--muted:#5c6f66;--green:#176b48;--green-dark:#105537;--line:#dce7df;--paper:#fff;--wash:#f4f7f1;--soft:#eaf4eb;--gold:#fff5d9;--error:#96432b}
*{box-sizing:border-box}
body{margin:0;background:var(--wash);color:var(--ink);font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;font-size:18px;line-height:1.55}
a{color:var(--green);text-underline-offset:4px}
button,input,select{font:inherit}
button{min-height:46px;border:1px solid var(--line);border-radius:12px;padding:10px 16px;background:#fff;color:var(--ink);font-weight:650;cursor:pointer;line-height:1.35}
button:hover{border-color:#87ac94;background:#f4faf4}
button:disabled{cursor:default;opacity:.72}
button.primary{background:var(--green);border-color:var(--green);color:#fff}
button.primary:hover{background:var(--green-dark)}
button.secondary{background:var(--soft);border-color:#c9ddce}
button.quiet{background:transparent;border-color:transparent;text-decoration:underline;text-underline-offset:4px;font-size:16px}
button:focus-visible,input:focus-visible,select:focus-visible,a:focus-visible,summary:focus-visible{outline:3px solid #d99a22;outline-offset:4px}
input,select{border:2px solid #b2c4b7;border-radius:10px;background:#fff;color:var(--ink);min-height:50px;padding:9px 12px;max-width:100%}
input{font-size:26px;width:140px;text-align:center;font-variant-numeric:tabular-nums}
select{font-size:17px}
label{display:block;font-size:18px;font-weight:650;margin-bottom:10px}
strong{font-weight:750}
.skip-link{position:absolute;left:15px;top:-80px;background:#fff;padding:12px;z-index:5}
.skip-link:focus{top:10px}
.site-header{max-width:1000px;margin:0 auto;padding:22px 28px;display:flex;gap:22px;align-items:center;font-size:15px}
.site-header>a:first-child{font-size:21px;font-weight:800;text-decoration:none;letter-spacing:-.5px}
.site-header>span{color:var(--muted)}
.other-topic{margin-left:auto;font-size:15px}
main{max-width:1000px;margin:0 auto;padding:0 28px 48px}
.task-card,.work-card,.settings{background:var(--paper);border:1px solid var(--line);border-radius:22px;padding:26px 30px;margin:0 0 18px;box-shadow:0 3px 0 #e9eee5}
.task-card{border-top:5px solid var(--green)}
.eyebrow{margin:0 0 6px;color:var(--muted);font-size:14px;font-weight:700;letter-spacing:.075em;text-transform:uppercase}
h1{font-size:clamp(28px,4.5vw,40px);line-height:1.2;margin:0;font-weight:780;letter-spacing:-.025em}
.task-numbers{display:block;font-size:clamp(42px,6vw,56px);line-height:1.18;margin:10px 0 16px;color:var(--green);font-variant-numeric:tabular-nums}
.definition{font-size:18px;margin:0 0 16px;max-width:770px}
.task-bottom{display:flex;align-items:center;gap:12px;flex-wrap:wrap}
.task-counter{font-size:15px;color:var(--muted)}
.mode-controls{display:flex;gap:8px;flex-wrap:wrap;margin:18px 0 0;padding-top:18px;border-top:1px solid var(--line)}
.mode-controls button{font-size:16px}
.mode-controls button[aria-pressed=true]{background:var(--soft);border-color:var(--green);box-shadow:inset 0 0 0 1px var(--green)}
.settings{padding:16px 22px;font-size:16px}
.settings summary{cursor:pointer;color:var(--muted);min-height:28px;font-weight:650}
.settings-grid{display:flex;gap:16px 24px;align-items:end;flex-wrap:wrap;margin-top:16px}
.settings label{font-size:16px;margin-bottom:6px}
.task-nav{display:flex;gap:8px}
.task-nav button{font-size:16px}
.stage-heading{display:flex;gap:12px;align-items:flex-start;margin-bottom:18px}
.stage-number{flex:0 0 33px;height:33px;display:grid;place-items:center;border-radius:50%;background:var(--green);color:#fff;font-size:16px;font-weight:800;margin-top:2px}
h2{font-size:24px;line-height:1.3;letter-spacing:-.015em;margin:0}
.stage-subtitle{margin:5px 0 0;font-size:17px;color:var(--muted)}
.factor-columns{display:grid;grid-template-columns:1fr 1fr;gap:18px;align-items:start}
.factor-column{border:1px solid var(--line);border-radius:16px;background:#fafcf8;padding:18px;min-width:0}
.factor-column.active{border:2px solid #90b39a;padding:17px;background:#f5fbf4}
.factor-column.done{border-color:#bdd5c3}
.column-heading{font-size:17px;font-weight:700;margin:0 0 14px;display:flex;justify-content:space-between;gap:8px;flex-wrap:wrap}
.column-heading .done-label{font-size:14px;color:var(--green)}
.ladder{margin:0 auto 12px;border-collapse:collapse;min-width:92px;font-size:30px;font-weight:700;font-variant-numeric:tabular-nums;line-height:1.25}
.ladder th,.ladder td{padding:4px 14px;text-align:right;min-width:48px}
.ladder th{font-weight:700;border-right:2px solid #658573}
.ladder td{text-align:left;font-weight:550;color:var(--green)}
.ladder .current th,.ladder .current td{background:#e1efdf}
.ladder .last th{color:var(--muted);font-size:25px}
.factor-expression{font-size:18px;text-align:center;margin:14px 0 0;overflow-wrap:anywhere}
.terminal-note{font-size:14px;color:var(--muted);margin:9px 0 0;text-align:center}
.active-calculation{background:#f3f8f1;border-radius:15px;padding:20px;margin-top:20px}
.input-row{display:flex;align-items:center;gap:12px;flex-wrap:wrap}
.number-input{width:125px}
.prime-choices{display:flex;flex-wrap:wrap;gap:6px;margin-top:13px;align-items:center}
.prime-choices span{flex-basis:100%;font-size:15px;color:var(--muted);margin-bottom:3px}
.prime-choices button{font-size:18px;min-width:44px;min-height:44px;padding:6px 10px;font-variant-numeric:tabular-nums}
.accepted-divisor{margin:0 0 8px;font-size:20px;font-weight:650}
.factor-row{display:flex;align-items:center;gap:9px;flex-wrap:wrap;padding:16px 0}
.factor-row+.factor-row{border-top:1px dashed var(--line)}
.factor-row-label{min-width:68px;font-size:24px;font-weight:750;font-variant-numeric:tabular-nums}
.factor-chip{min-width:53px;min-height:56px;position:relative;font-size:25px;font-weight:700;padding:8px 14px;border:2px solid #cbd8cb;border-radius:12px;background:#fff}
.factor-chip.pending{border-color:#cb8f22;box-shadow:0 0 0 2px #ffe5ad}
.factor-chip.paired{background:#e8f3e9;border-color:#83ac90;color:var(--green);opacity:1}
.factor-chip.selected{background:var(--green);border-color:var(--green);color:#fff}
.factor-chip small{display:block;font-size:10px;font-weight:700;line-height:1.1;margin-top:3px}
.times{font-size:22px;color:var(--muted)}
.pair-list{display:flex;gap:8px;flex-wrap:wrap;margin:14px 0}
.pair-tag{font-size:15px;color:var(--green);background:var(--soft);border:1px solid #c4ddcb;padding:6px 10px;border-radius:9px}
.rule-box{background:var(--gold);padding:17px 20px;border:1px solid #ebddae;border-radius:13px;margin:18px 0;font-size:18px}
.rule-box p{margin:0}
.result-expression{font-size:clamp(24px,3.8vw,32px);line-height:1.6;margin:18px 0;overflow-wrap:anywhere;font-weight:700}
.selection-explanation{margin:12px 0;font-size:16px;color:var(--muted)}
.confirmation-row{display:flex;gap:10px;flex-wrap:wrap;align-items:center;margin-top:18px}
.confirmation-row>.quiet{font-size:15px}
.accepted-caption{display:flex;gap:9px;align-items:center;color:var(--green);font-size:16px;margin:16px 0 0}
.check-mark{font-size:20px;font-weight:800}
.feedback{padding:13px 16px;border-radius:12px;margin:16px 0 0;font-size:17px;border:1px solid transparent}
.feedback.error{background:#fff3e8;border-color:#edcdb3;color:#77412d}
.feedback.success{background:#edf7e9;border-color:#b7d7b9;color:#225c36}
.feedback.info{background:#f0f5f1;border-color:var(--line)}
.feedback:empty{display:none}
.hint-box{background:#fff9e9;border:1px solid #e9dbb1;border-radius:14px;padding:18px 20px;margin-top:18px;font-size:18px}
.hint-box p{margin:0 0 12px}
.hint-box p:last-child{margin-bottom:0}
.hint-box .quiet{padding-left:0;color:#71531a}
.hint-detail{border-top:1px solid #e6d7ad;padding-top:12px;font-weight:600}
.help-marker{font-size:14px;color:var(--muted)}
.independent-note{color:var(--muted);font-size:16px;margin:0 0 18px}
.fresh-row{margin-top:18px;border-top:1px solid var(--line);padding-top:18px;display:flex;gap:14px;flex-wrap:wrap;align-items:center}
.fresh-row button{font-size:16px}
.answer-proof{font-size:20px;margin:12px 0 0;line-height:1.7;overflow-wrap:anywhere}
.visually-hidden{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
body.embedded .site-header{display:none}
body.embedded .public-explanation{display:none}
body.embedded main{padding-top:14px}
@media(max-width:650px){.site-header{padding:17px 18px;gap:15px}.other-topic{display:none}main{padding:0 16px 32px}.task-card,.work-card{padding:22px 20px;border-radius:18px}.task-card{border-top-width:4px}.factor-columns{gap:12px}.factor-column{padding:13px 9px}.factor-column.active{padding:12px 8px}.factor-expression{font-size:17px}.column-heading{font-size:15px}.ladder{font-size:29px}.stage-heading{gap:10px}h2{font-size:22px}.rule-box{padding:15px}.factor-row-label{min-width:55px;font-size:22px}.factor-chip{min-width:48px;padding:7px 11px}.active-calculation{padding:17px}.settings{padding:14px 18px}.settings-grid{gap:15px}.site-header>span{font-size:14px}}
@media(max-width:390px){.site-header{padding-inline:13px}main{padding-inline:10px}.task-card,.work-card{padding:19px 15px}.mode-controls button{font-size:15px;padding:9px 12px}.factor-columns{gap:8px}.ladder th,.ladder td{padding-inline:11px}.factor-expression{font-size:16px}.input-row{gap:9px}.input-row button{padding-inline:12px}.number-input{width:105px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important}}
@media print{body{background:#fff}.site-header,.settings,.mode-controls,.task-bottom,.confirmation-row,.input-row button,.prime-choices,.fresh-row,.skip-link{display:none}.task-card,.work-card{box-shadow:none;break-inside:avoid}main{padding:0;max-width:none}.hint-box{background:#fff}.factor-chip{print-color-adjust:exact}}