:root { color-scheme: light; font-family: 'Avenir Next', Avenir, 'Segoe UI', sans-serif; color: #202326; background: #f5f4f0; }
* { box-sizing: border-box; }
body { margin: 0; }
a { color: inherit; }
.library-header, main, footer { max-width: 1080px; margin: auto; padding: 0 28px; }
.library-header { padding-top: 32px; padding-bottom: 26px; }
.back-link { font-size: 14px; text-underline-offset: 4px; }
.eyebrow { margin: 38px 0 8px; font-size: 11px; font-weight: 700; letter-spacing: .16em; text-transform: uppercase; }
h1 { font-size: clamp(30px,5vw,48px); letter-spacing: -.045em; line-height: 1.1; margin: 0 0 16px; font-weight: 600; }
.intro { margin: 0; color: #555957; font-size: 16px; }
.toolbar { display: flex; align-items: end; gap: 12px; padding: 20px 0; border-top: 1px solid #d8d8d2; border-bottom: 1px solid #d8d8d2; }
label { display: flex; flex-direction: column; gap: 6px; font-size: 12px; font-weight: 600; }
select, input, button { font: inherit; font-size: 14px; color: inherit; border: 1px solid #aaa; border-radius: 6px; padding: 11px 12px; background: white; min-height: 44px; }
select { width: 285px; max-width: 100%; }
.search-field { flex: 1; min-width: 100px; }
input { width: 100%; }
button { cursor: pointer; white-space: nowrap; }
button.primary { background: #202326; color: white; border-color: #202326; }
button:disabled { opacity: .5; cursor: default; }
:focus-visible { outline: 3px solid #446995; outline-offset: 3px; }
.results-meta { display: flex; justify-content: space-between; align-items: center; font-size: 12px; color: #646864; padding: 6px 0; }
.flashcard { position: relative; background: white; border: 1px solid #999; padding: 60px 38px 38px; margin-bottom: 24px; display: grid; grid-template-columns: 1fr 1.07fr; gap: 32px; min-height: 375px; }
.card-number { position: absolute; right: 28px; top: 16px; font-size: 14px; color: #666; text-decoration: none; font-variant-numeric: tabular-nums; }
.card-number:hover { text-decoration: underline; }
.card-story { font-size: 23px; line-height: 1.45; }
.card-story p { margin: 0 0 5px; }
.card-story .question { margin-top: 25px; font-weight: 600; }
.card-story .question:first-child { margin-top: 0; }
mark { color: inherit; background: #fff0b7; font-weight: 600; white-space: nowrap; padding: 1px 0; }
.card-work { border-left: 1px solid #dcdcdc; padding-left: 24px; }
.diagram { display: block; width: 100%; height: auto; fill: currentColor; margin-bottom: 10px; overflow: visible; }
.calculation { display: flex; align-items: center; gap: 20px; margin: 0 0 10px; }
.operation { flex: 0 0 43%; padding: 11px 12px; font-weight: 600; font-size: 19px; border-radius: 6px; }
.addition { background: #ddebf8; }
.subtraction { background: #fbe4cd; }
.equation { font-size: 31px; font-weight: 600; white-space: nowrap; letter-spacing: -.025em; }
.two-steps .equation { font-size: 28px; }
.answer { font-size: 18px; line-height: 1.4; margin: 18px 0 0; }
footer { padding-top: 8px; padding-bottom: 40px; color: #646864; font-size: 12px; }
.empty { padding: 36px 0; }
@media (max-width: 900px) { .toolbar { flex-wrap: wrap; } .toolbar label { flex: 1 1 40%; } select { width: 100%; } .flashcard { padding: 48px 24px 28px; gap: 22px; } .card-story { font-size: 20px; } .operation { font-size: 16px; padding: 10px; } .equation,.two-steps .equation { font-size: 25px; } .calculation { gap: 12px; } }
@media (max-width: 620px) { .library-header,main,footer { padding-left: 18px; padding-right: 18px; } .toolbar label { flex-basis: 100%; } .toolbar button { flex: 1; } .results-meta span { display: none; } .flashcard { grid-template-columns: 1fr; gap: 22px; padding: 44px 22px 26px; } .card-work { border-left: 0; border-top: 1px solid #dcdcdc; padding: 18px 0 0; } .card-story { font-size: 20px; } .card-story .question { margin-top: 18px; } .card-number { right: 20px; top: 12px; font-size: 12px; } .diagram { max-width: 430px; margin: 0 auto 12px; } .operation { font-size: 17px; } .equation,.two-steps .equation { font-size: 28px; } .answer { font-size: 17px; } }
@page { size: letter; margin: .625in .75in; }
@media print {
    :root { background: white; print-color-adjust: exact; -webkit-print-color-adjust: exact; }
    .library-header,.toolbar,.results-meta,footer,noscript { display: none; }
    main { width: 7in; max-width: none; padding: 0; margin: 0; }
    .flashcard { width: 7in; height: 3.083in; min-height: 0; padding: .42in .278in .20in; margin: 0 0 .25in; grid-template-columns: 3in 1fr; gap: .25in; break-inside: avoid; border: .65pt solid #777; }
    .flashcard:nth-child(3n) { margin-bottom: 0; break-after: page; }
    .flashcard:last-child { break-after: auto; margin-bottom: 0; }
    .card-number { top: .15in; right: .22in; font-size: 9pt; }
    .card-story { font-size: 13pt; line-height: 1.42; }
    .card-story .question { margin-top: 15pt; }
    .card-work { border-top: 0; border-left: .5pt solid #dcdcdc; padding: 0 0 0 .18in; }
    .diagram { margin: 0 0 4pt; max-width: none; }
    .calculation { gap: 12pt; margin-bottom: 5pt; }
    .operation { padding: 6pt 7pt; font-size: 11pt; border-radius: 4pt; }
    .equation { font-size: 20pt; }
    .two-steps .equation { font-size: 18pt; }
    .answer { font-size: 10.5pt; margin-top: 9pt; line-height: 1.3; }
}