:root {
  --paper: #f4f7fb;
  --sheet: #ffffff;
  --ink: #14243a;
  --soft: #3f4f66;
  --line: #c9d5e4;
  --margin: #e4a3a3;
  --red: #b3261e;
  --blue: #1d4f91;
  --focus: #1d4f91;
  --slab: Rockwell, "Rockwell Nova", "Roboto Slab", "Zilla Slab", "DejaVu Serif", Georgia, serif;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --paper: #111a26;
    --sheet: #172334;
    --ink: #e6edf6;
    --soft: #b4c2d4;
    --line: #2f4058;
    --margin: #6b3a3f;
    --red: #ff8f86;
    --blue: #9cc3ff;
    --focus: #9cc3ff;
  }
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 400 1.0625rem/1.55 var(--sans);
}
a { color: var(--blue); text-underline-offset: 2px; }
a:focus-visible, button:focus-visible, summary:focus-visible, input:focus-visible, select:focus-visible {
  outline: 3px solid var(--focus); outline-offset: 2px;
}
.vh { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

.top, main, .site-foot { max-width: 46rem; margin: 0 auto; padding: 0 16px; }
.top { padding-top: 2rem; }
h1, h2, h3 { font-family: var(--slab); line-height: 1.2; font-weight: 700; }
h1 { font-size: clamp(1.75rem, 1.2rem + 2.6vw, 2.6rem); margin: 0 0 .6rem; letter-spacing: -.01em; }
h1::after { content: ""; display: block; width: 4.5rem; height: 3px; margin-top: .7rem; background: var(--red); border-radius: 2px; transform: rotate(-1.2deg); }
.lede { margin: 0 0 1.4rem; font-size: 1.125rem; color: var(--soft); max-width: 38rem; }
h2 { font-size: 1.375rem; margin: 2.2rem 0 .6rem; }
h3 { font-size: 1.125rem; margin: 1.4rem 0 .3rem; }

/* The question */
.ask { background: var(--sheet); border: 1px solid var(--line); border-radius: 10px; padding: 1rem 1rem 1.1rem; }
.seg { border: 0; margin: 0 0 .9rem; padding: 0; display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; }
.seg legend { padding: 0; margin-bottom: .4rem; font-weight: 600; width: 100%; }
.seg label { position: relative; }
.seg input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.seg span { display: inline-block; min-width: 4.2rem; text-align: center; padding: .5rem .9rem; border: 1.5px solid var(--soft); border-radius: 999px; font-weight: 600; }
.seg input:checked + span { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.seg input:focus-visible + span { outline: 3px solid var(--focus); outline-offset: 2px; }
.years { display: flex; flex-wrap: wrap; gap: .8rem 1.4rem; align-items: end; }
.yr label { display: block; font-weight: 600; margin-bottom: .3rem; }
input[type=text], select {
  font: 600 1.5rem/1.2 var(--slab); color: var(--ink); background: var(--paper);
  border: 1.5px solid var(--soft); border-radius: 8px; padding: .45rem .6rem;
}
input[type=text] { width: 6.5ch; letter-spacing: .04em; }
select { font-size: 1.25rem; padding-right: .4rem; }
input[aria-invalid=true] { border-color: var(--red); }
.stepper { display: flex; gap: .4rem; align-items: stretch; }
.step {
  min-width: 48px; min-height: 48px; font: 600 1.5rem/1 var(--sans); color: var(--ink); background: var(--paper);
  border: 1.5px solid var(--soft); border-radius: 8px; cursor: pointer; touch-action: manipulation;
}
.step:hover { background: var(--sheet); }
.err { color: var(--red); font-weight: 600; margin: .6rem 0 0; }

/* The answer */
.result { margin-top: 1.2rem; }
.headline { font: 700 1.3rem/1.35 var(--slab); margin: 0 0 .8rem; }
.actions { display: flex; flex-wrap: wrap; gap: .6rem; align-items: center; }
.btn {
  font: 600 1rem/1 var(--sans); color: var(--ink); background: transparent; cursor: pointer;
  border: 1.5px solid var(--ink); border-radius: 8px; padding: .65rem .9rem; min-height: 44px;
}
.btn:hover { background: var(--sheet); }
.copied { color: var(--soft); }
.tools { margin: 1.2rem 0; }
.lessons > .tools { margin: 1.6rem 0 .4rem; }
.cmp-box { margin-top: 1rem; }
.today { color: var(--soft); white-space: nowrap; }
.print-only { display: none; }
.cmp-box > summary { cursor: pointer; font-weight: 600; color: var(--blue); padding: .4rem 0; }
.cmp-box .yr { margin: .5rem 0 0; }
.cmp { width: 100%; border-collapse: collapse; margin-top: 1rem; font-size: 1rem; }
.cmp th, .cmp td { text-align: left; vertical-align: top; padding: .5rem .5rem .5rem 0; border-bottom: 1px solid var(--line); }
.cmp thead th { font-family: var(--slab); font-size: 1.0625rem; }
.cmp tbody th { font-weight: 600; }

/* The lessons: a ruled notebook page with a red margin line */
.lessons h2 { margin-top: 2rem; }
.lesson { border-top: 1px solid var(--line); }
.lessons h2 + .lesson { border-top-width: 2px; border-top-color: var(--ink); }
.lesson > summary {
  list-style: none; cursor: pointer; padding: .75rem 0; display: flex; flex-wrap: wrap; gap: .1rem 1rem;
  justify-content: space-between; align-items: baseline;
}
.lesson > summary::-webkit-details-marker { display: none; }
.lesson > summary .name { font: 700 1.125rem/1.3 var(--slab); }
.lesson > summary .name::before { content: "+"; display: inline-block; width: 1.2rem; color: var(--red); font-family: var(--sans); }
.lesson[open] > summary .name::before { content: "\2212"; }
.lesson > summary .note { color: var(--soft); }
.body { padding: 0 0 1rem; }
.show-all { margin: .4rem 0 0; }
.row { display: grid; grid-template-columns: 3.4rem 1fr; gap: .8rem; margin: 0 0 .55rem; padding-left: 0; }
.row .k { font: 700 1rem/1.55 var(--slab); color: var(--soft); border-right: 2px solid var(--margin); padding-right: .6rem; }
.row.then s { text-decoration-color: var(--red); text-decoration-thickness: 2px; }
.row.then > span { position: relative; }
.row.then > .drawing > s:not(.strike-ink) { text-decoration-color: transparent; }
.strike-ink { position: absolute; inset: 0; color: transparent; pointer-events: none; transform-origin: 0 50%; }
.row.now .k { color: var(--red); }
.row.chg .k { color: var(--ink); }
.src { white-space: normal; }
.range { margin: .5rem 0 0 4.2rem; color: var(--soft); }
.later { margin: 0 0 .55rem; }
.later > summary { cursor: pointer; color: var(--blue); font-weight: 600; padding: .2rem 0 .2rem 4.2rem; }
.later[open] > summary { margin-bottom: .5rem; }

.prose { margin-top: 1rem; }
.prose p { max-width: 40rem; }
.faq h3 + p { margin-top: 0; }

/* Shared footer */
.site-foot { margin-top: 3rem; padding-top: 1.2rem; padding-bottom: 2rem; border-top: 1px solid var(--line); color: var(--soft); }
.sb-footer p { margin: 0 0 .8rem; }
.sb-more { line-height: 1.8; }
.sb-privacy, .sb-credit { font-size: 1rem; }

@media (max-width: 30rem) {
  .cmp thead { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); }
  .cmp, .cmp tbody, .cmp tr, .cmp th, .cmp td { display: block; }
  .cmp tr { padding: .5rem 0; border-bottom: 1px solid var(--line); }
  .cmp th, .cmp td { border: 0; padding: 0; }
  .cmp td::before { content: attr(data-y) ": "; font-weight: 600; color: var(--soft); }
  .row { grid-template-columns: 2.9rem 1fr; gap: .6rem; }
  .range { margin-left: 0; }
  .later > summary { padding-left: 0; }
  .headline { font-size: 1.125rem; }
  .top { padding-top: 1.1rem; }
  h1 { font-size: 1.6rem; }
  h1::after { margin-top: .5rem; }
  .lede { font-size: 1.0625rem; margin-bottom: 1rem; }
  .ask { padding: .8rem .8rem .9rem; }
  .seg { margin-bottom: .6rem; }
}

@media print {
  :root { --paper: #fff; --sheet: #fff; --ink: #000; --soft: #333; --line: #bbb; --margin: #d99; --red: #a11; --blue: #000; }
  body { font-size: 10.5pt; line-height: 1.45; background: #fff; }
  @page { margin: 14mm 14mm 16mm; }
  .top, main { max-width: none; padding: 0; }
  .lede, .ask, .actions, .cmp-box > summary, .prose, .site-foot, .lesson > summary .name::before { display: none; }
  .cmp-box:not([open]) { display: none; }
  .cmp-box .yr { display: none; }
  h1 { font-size: 20pt; }
  h1::after { display: none; }
  .lesson { break-inside: avoid; }
  /* On paper only what changed or may have changed for this class. */
  .g-current, .g-before, .g-none, .lesson.s-current, .lesson.s-before, .lesson.s-none { display: none !important; }
  .stepper .step, .strike-ink, .ghost, .show-all, .later > summary { display: none !important; }
  .row.then > .drawing > s:not(.strike-ink) { text-decoration-color: var(--red); }
  .lessons h2 { break-after: avoid; }
  a { text-decoration: none; }
  .src a[data-short]::after { content: " " attr(data-short); word-break: break-all; }
  .print-only { display: block; margin: 0 0 .3rem; color: var(--soft); }
  .tools { margin: 0; }
}