/* Acca Arithmetic — an exercise book. Layers: fonts, tokens, base, header, cover,
   chapter head, book grid, problems, side card, contents, formula sheet, sketches, footer, narrow. */

@font-face { font-family: "Bitter"; src: url("fonts/bitter-latin-wght-normal.woff2") format("woff2"); font-weight: 100 900; font-display: swap; unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+20AC, U+2122, U+2212, U+2215; }
@font-face { font-family: "Bitter"; src: url("fonts/bitter-latin-ext-wght-normal.woff2") format("woff2"); font-weight: 100 900; font-display: swap; unicode-range: U+0100-02BA, U+20A0-20AB, U+20AD-20C0; }
@font-face { font-family: "Karla"; src: url("fonts/karla-latin-wght-normal.woff2") format("woff2"); font-weight: 200 800; font-display: swap; unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+20AC, U+2122, U+2212, U+2215; }
@font-face { font-family: "Karla"; src: url("fonts/karla-latin-wght-italic.woff2") format("woff2"); font-weight: 200 800; font-style: italic; font-display: swap; }
@font-face { font-family: "Karla"; src: url("fonts/karla-latin-ext-wght-normal.woff2") format("woff2"); font-weight: 200 800; font-display: swap; unicode-range: U+0100-02BA, U+20A0-20AB, U+20AD-20C0; }
@font-face { font-family: "Caveat"; src: url("fonts/caveat-latin-wght-normal.woff2") format("woff2"); font-weight: 400 700; font-display: swap; }

:root {
  --paper: #fdfdfb;
  --wash: #f1f5fb;
  --rule: #d6e2f0;
  --rule-faint: #e4ecf6;
  --margin: #e2a5a0;
  --ink: #2f343a;
  --ink-soft: #5b626b;
  --pen: #1f47a8;
  --red: #b8322a;
  --highlight: #fff1a8;

  --slab: "Bitter", "Rockwell", Georgia, serif;
  --sans: "Karla", "Helvetica Neue", Arial, sans-serif;
  --hand: "Caveat", "Bradley Hand", "Segoe Print", cursive;

  --s-1: clamp(1.25rem, 1.1rem + 0.6vw, 1.5rem);
  --s-2: clamp(1.55rem, 1.25rem + 1.3vw, 2.15rem);
  --s-3: clamp(2.1rem, 1.4rem + 3vw, 3.5rem);
  --s-cover: clamp(2.7rem, 1.4rem + 5.5vw, 5.4rem);
  --gap: clamp(1rem, 0.6rem + 1.6vw, 2rem);
  --ruled: repeating-linear-gradient(to bottom, transparent 0 calc(1.75rem - 1px), var(--rule-faint) calc(1.75rem - 1px) 1.75rem);
}

*, *::before, *::after { box-sizing: border-box; }
html { overflow-wrap: break-word; -webkit-text-size-adjust: 100%; scroll-padding-block-start: 1rem; }
@media (prefers-reduced-motion: no-preference) { html { scroll-behavior: smooth; } }
body { margin: 0; background: var(--paper); color: var(--ink); font: 400 1.0625rem/1.65 var(--sans); }
h1, h2, h3 { font-family: var(--slab); line-height: 1.15; margin: 0; color: var(--pen); }
p, ol, ul, dl, figure { margin: 0; }
a { color: var(--pen); text-decoration-thickness: 1px; text-underline-offset: 0.2em; }
@media (hover: hover) and (pointer: fine) { a:hover { color: var(--red); } }
:focus-visible { outline: 3px solid var(--red); outline-offset: 3px; border-radius: 2px; }
sup { font-size: 0.7em; line-height: 0; }
.vh { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
.skip { position: absolute; inset-inline-start: 1rem; inset-block-start: -3rem; background: var(--pen); color: #fff; padding: 0.5rem 0.9rem; z-index: 5; }
.skip:focus { inset-block-start: 1rem; }
.kicker, .chap-no { font: 700 0.8rem/1.2 var(--sans); letter-spacing: 0.14em; text-transform: uppercase; color: var(--red); margin-block-end: 0.5rem; }
.label { font: 700 0.72rem/1 var(--sans); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-soft); margin-inline-end: 0.4rem; }

/* Header */
.top { background: #fff; border-block-end: 3px double var(--pen); }
.top-inner { max-width: 76rem; margin-inline: auto; padding: 0.9rem var(--gap); display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 0.6rem 2rem; }
.brand { display: grid; text-decoration: none; }
.brand-name { font: 800 1.45rem/1.1 var(--slab); color: var(--pen); }
.brand-tag { font: 400 1.05rem/1.2 var(--hand); color: var(--red); }
.chapters ul { list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 0.2rem 1.15rem; }
.chapters a { display: inline-block; padding-block: 0.3rem; font-weight: 600; font-size: 0.95rem; color: var(--ink); text-decoration: none; }
.chapters a[aria-current="page"] { color: var(--red); text-decoration: underline wavy var(--red) 1px; text-underline-offset: 0.35em; }
.menu { display: none; }
.menu summary { list-style: none; cursor: pointer; font: 700 0.85rem/1 var(--sans); letter-spacing: 0.1em; text-transform: uppercase; padding: 0.65rem 0.9rem; border: 1.5px solid var(--pen); border-radius: 4px; color: var(--pen); }
.menu summary::-webkit-details-marker { display: none; }
.menu summary::after { content: " ▾"; }
.menu[open] summary::after { content: " ▴"; }
.menu .chapters ul { flex-direction: column; gap: 0; padding-block-start: 0.5rem; }
.menu .chapters a { display: block; padding-block: 0.55rem; border-block-end: 1px solid var(--rule); font-size: 1.05rem; }

/* Cover (index) */
.cover { background: #fff var(--ruled); border-block-end: 1px solid var(--rule); }
.cover-inner { max-width: 76rem; margin-inline: auto; padding: clamp(2rem, 1rem + 4vw, 4.5rem) var(--gap); display: flex; flex-wrap: wrap; align-items: center; gap: 2rem 3rem; }
.cover-text { flex: 1 1 26rem; min-inline-size: 0; }
.cover h1 { font-size: var(--s-cover); font-weight: 800; letter-spacing: -0.015em; }
.cover .sub { font-size: 1.15rem; max-inline-size: 36rem; margin-block-start: 1rem; }
.cover-fig { flex: 1 1 20rem; max-inline-size: 29rem; background: #fff; }

/* Chapter head */
.chapter-head { background: #fff var(--ruled); border-block-end: 1px solid var(--rule); }
.head-inner { max-width: 76rem; margin-inline: auto; padding: clamp(1.6rem, 1rem + 2.5vw, 3rem) var(--gap) 1.75rem calc(var(--gap) + 5.5rem); position: relative; }
.head-inner::before { content: ""; position: absolute; inset-block: 0; inset-inline-start: calc(var(--gap) + 4.4rem); border-inline-start: 2px solid var(--margin); }
.chapter-head h1 { font-size: var(--s-3); font-weight: 800; }
.lede { font-size: 1.12rem; max-inline-size: 42rem; margin-block-start: 0.9rem; }
.range { font: 600 0.9rem/1.4 var(--sans); color: var(--ink-soft); margin-block-start: 0.9rem; }

/* Book grid: margin + problems + side card */
.book { max-width: 76rem; margin-inline: auto; padding: 1.5rem var(--gap) 3rem; display: flex; flex-wrap: wrap; gap: 2rem clamp(2rem, 1rem + 3vw, 4rem); }
.problems { flex: 1 1 34rem; min-inline-size: 0; max-inline-size: 46rem; }
.side { flex: 0 1 19rem; align-self: start; position: sticky; top: 1rem; display: grid; gap: 1.25rem; }
.margin-note { font: 600 1.45rem/1 var(--hand); color: var(--red); padding-inline-start: 5.5rem; margin-block-end: -0.5rem; transform: rotate(-2deg); transform-origin: left; }

/* Problems */
.problem { display: grid; grid-template-columns: 4.4rem minmax(0, 1fr); column-gap: 1.1rem; padding-block: 1.75rem; border-block-end: 1px solid var(--rule); }
.num { white-space: nowrap; font: 700 2.5rem/1 var(--hand); color: var(--red); text-align: end; padding-inline-end: 0.9rem; border-inline-end: 2px solid var(--margin); padding-block-start: 0.1rem; }
.problem-body > * + * { margin-block-start: 0.7rem; }
.ptitle { font-size: var(--s-1); font-weight: 700; color: var(--ink); }
.level { display: inline-flex; align-items: center; gap: 0.45rem; font: 700 0.75rem/1 var(--sans); letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-soft); }
.dots { display: inline-flex; gap: 3px; }
.dots i { inline-size: 0.55rem; block-size: 0.55rem; border-radius: 50%; border: 1.5px solid var(--pen); }
.dots i.on { background: var(--pen); }
.statement { max-inline-size: 40rem; }
.given { display: flex; flex-wrap: wrap; gap: 0.4rem 0.6rem; }
.given div { background: var(--wash); border: 1px solid var(--rule); border-radius: 4px; padding: 0.3rem 0.65rem; font-variant-numeric: tabular-nums; }
.given dt { display: inline; font: 700 0.72rem/1 var(--sans); letter-spacing: 0.08em; text-transform: uppercase; color: var(--ink-soft); margin-inline-end: 0.35rem; }
.given dd { display: inline; margin: 0; font-weight: 600; }
.working summary { display: inline-flex; align-items: center; gap: 0.5rem; cursor: pointer; font: 700 0.95rem/1 var(--sans); color: var(--pen); padding: 0.6rem 0.95rem; border: 1.5px solid var(--pen); border-radius: 2rem; list-style: none; }
.working summary::-webkit-details-marker { display: none; }
.working summary::before { content: "+"; font-size: 1.1rem; line-height: 1; }
.working[open] summary::before { content: "−"; }
.working[open] summary { background: var(--pen); color: #fff; }
@media (hover: hover) and (pointer: fine) { .working summary:hover { background: var(--wash); } .working[open] summary:hover { background: var(--pen); } }
.steps { margin-block-start: 1rem; padding: 0.9rem 1rem 0.9rem 2.4rem; background: #fff var(--ruled); background-position: 0 0.9rem; border: 1px solid var(--rule); border-radius: 4px; line-height: 1.75rem; font-variant-numeric: tabular-nums; }
.steps li::marker { font: 700 1.1em var(--hand); color: var(--red); }
.answer { margin-block-start: 0.9rem; padding: 0.7rem 0.9rem; border: 2px solid var(--red); border-radius: 1.2rem 0.4rem 1.1rem 0.5rem; font-variant-numeric: tabular-nums; }
.answer-label { font: 700 1.35rem/1 var(--hand); color: var(--red); margin-inline-end: 0.35rem; }

.turns { margin-block-start: 2.5rem; }
.turn { display: inline-grid; gap: 0.15rem; text-decoration: none; font: 700 var(--s-1)/1.2 var(--slab); }
.turn span { font: 600 1.15rem/1 var(--hand); color: var(--red); }

/* Side card */
.card { background: #fff; border: 1px solid var(--rule); border-block-start: 4px solid var(--red); border-radius: 3px; padding: 1rem 1.1rem 1.1rem; box-shadow: 0 1px 0 var(--rule), 0 6px 18px -12px rgba(31, 71, 168, 0.35); }
.card-title { font: 700 0.78rem/1.3 var(--sans); letter-spacing: 0.12em; text-transform: uppercase; color: var(--red); margin-block-end: 0.6rem; }
.f-list { list-style: none; padding: 0; display: grid; gap: 0.75rem; }
.f-list li { display: grid; gap: 0.1rem; padding-block-end: 0.65rem; border-block-end: 1px dashed var(--rule); }
.f-list li:last-child { border: 0; padding: 0; }
.f-name { font: 700 0.98rem/1.3 var(--slab); color: var(--ink); }
.f-rule { color: var(--pen); font-weight: 600; }
.f-eg { font-size: 0.9rem; color: var(--ink-soft); font-variant-numeric: tabular-nums; }
.jump ol { list-style: none; padding: 0; display: grid; gap: 0.2rem; font-size: 0.93rem; }
.jump a { color: var(--ink); text-decoration: none; display: flex; gap: 0.5rem; }
@media (hover: hover) and (pointer: fine) { .jump a:hover { color: var(--red); } }
.jn { font: 700 1.1rem/1.2 var(--hand); color: var(--red); min-inline-size: 1.4rem; text-align: end; }
.side-link { font-weight: 600; padding-inline-start: 0.2rem; }

/* Contents (index) */
.toc, .how { margin-block-start: 2.75rem; }
.toc h2, .how h2, .notation h2, .prose h2 { font-size: var(--s-2); font-weight: 700; }
.toc-list { list-style: none; padding: 0; margin-block-start: 1rem; display: grid; gap: 0.35rem; }
.toc-list a { display: flex; align-items: baseline; gap: 0.75rem; text-decoration: none; color: var(--ink); padding-block: 0.4rem 0; }
.toc-no { font: 700 1.8rem/1 var(--hand); color: var(--red); min-inline-size: 1.6rem; }
.toc-title { font: 700 1.2rem/1.3 var(--slab); color: var(--pen); }
.toc-leader { flex: 1; border-block-end: 2px dotted var(--rule); min-inline-size: 1rem; transform: translateY(-0.3rem); }
.toc-range { font-weight: 700; font-variant-numeric: tabular-nums; }
.toc-mix { padding-inline-start: 2.35rem; font-size: 0.88rem; color: var(--ink-soft); }
@media (hover: hover) and (pointer: fine) { .toc-list a:hover .toc-title { color: var(--red); } }
.how-list { margin-block-start: 1rem; padding-inline-start: 1.5rem; display: grid; gap: 0.5rem; }
.how-list li::marker { font: 700 1.2em var(--hand); color: var(--red); }

/* Formula sheet, about, 404 */
.sheet { max-width: 76rem; margin-inline: auto; padding: 2rem var(--gap) 3rem; }
.fcards { list-style: none; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 17rem), 1fr)); gap: 1.1rem; }
.fcard { background: #fff var(--ruled); background-position: 0 2.6rem; border: 1px solid var(--rule); border-block-start: 4px solid var(--red); border-radius: 3px; padding: 0.9rem 1rem 1rem; display: grid; gap: 0.35rem; align-content: start; }
.fcard .f-name { font-size: 1.08rem; }
.notation { margin-block-start: 3rem; max-inline-size: 46rem; }
.notation dl { margin-block-start: 1rem; display: grid; gap: 0.8rem; }
.notation dt { font: 700 1.05rem/1.3 var(--slab); color: var(--ink); }
.notation dd { margin: 0.15rem 0 0; }
.prose { max-inline-size: 46rem; }
.prose > * + * { margin-block-start: 1rem; }
.prose h2 { margin-block-start: 2.2rem; }
.pills { list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 0.6rem; }
.pills a { display: inline-block; padding: 0.5rem 1rem; border: 1.5px solid var(--pen); border-radius: 2rem; text-decoration: none; font-weight: 700; }

/* Sketches */
.sketch-fig { margin-block: 0.5rem 1rem; padding: 0.9rem 1rem; border: 1px solid var(--rule); border-radius: 4px; background: #fff; max-inline-size: 30rem; }
.sketch-fig figcaption { font: 600 1.15rem/1.3 var(--hand); color: var(--red); margin-block-start: 0.3rem; }
.sketch { display: block; inline-size: 100%; block-size: auto; }
.sketch .box { fill: #fff; stroke: var(--ink); stroke-width: 1.5; }
.sketch .answer-box { fill: none; stroke: var(--red); stroke-width: 2.5; }
.sketch .big { font: 700 22px var(--slab); fill: var(--ink); }
.sketch .big.red { fill: var(--red); }
.sketch .op { font: 700 20px var(--sans); fill: var(--ink-soft); }
.sketch .pen { font: 700 20px var(--hand); fill: var(--red); }
.sketch .note { font: 500 14px var(--sans); fill: var(--ink-soft); }
.sketch .small { font: 700 14px var(--sans); fill: var(--ink); }
.sketch .small.soft { font-weight: 500; fill: var(--ink-soft); }
.sketch .halo { paint-order: stroke; stroke: #fff; stroke-width: 5px; stroke-linejoin: round; }
.sketch .pen.big-pen { font-size: 26px; }
.sketch .arrow { fill: none; stroke: var(--ink); stroke-width: 1.5; stroke-linecap: round; stroke-linejoin: round; }
.sketch .bar { fill: var(--wash); stroke: var(--pen); stroke-width: 1.5; }
.sketch .axis { stroke: var(--ink); stroke-width: 1.5; }
.sketch .half { stroke: var(--red); stroke-width: 1.5; stroke-dasharray: 5 4; }
.sketch .strike { stroke: var(--red); stroke-width: 3; stroke-linecap: round; }
.sketch .edge { stroke: var(--pen); stroke-width: 1.75; }
.sketch .node { fill: #fff; stroke: var(--ink); stroke-width: 1.5; }
.sketch .seg-stake { fill: var(--wash); stroke: var(--ink); stroke-width: 1.25; }
.sketch .seg-profit { fill: #fff; stroke: var(--pen); stroke-width: 1.5; }
.sketch .seg-add { fill: var(--highlight); stroke: var(--red); stroke-width: 1.5; }

/* Footer */
.foot { background: #fff; border-block-start: 3px double var(--pen); }
.foot-inner { max-width: 76rem; margin-inline: auto; padding: 1.5rem var(--gap) 2rem; display: grid; gap: 0.5rem; font-size: 0.92rem; color: var(--ink-soft); }
.foot strong { color: var(--pen); font-family: var(--slab); }

/* Narrow */
@media (max-width: 52rem) {
  .side { position: static; flex-basis: 100%; }
}
@media (max-width: 47.99rem) {
  .wide-nav { display: none; }
  .menu { display: block; flex-basis: 100%; }
  .problem { grid-template-columns: 3.1rem minmax(0, 1fr); column-gap: 0.75rem; }
  .num { font-size: 1.85rem; padding-inline-end: 0.5rem; }
  .head-inner { padding-inline-start: calc(var(--gap) + 3.85rem); }
  .head-inner::before { inset-inline-start: calc(var(--gap) + 3.1rem); }
  .margin-note { padding-inline-start: 0.5rem; }
  .toc-mix { padding-inline-start: 2.35rem; }
}