/* Radiography Math Practice: a film viewer and an exposure console. Cool blue-white viewbox light, deep navy ink,
   problem numbers in a dark console strip with phosphor-green digits, and a lead-grey rule down the film edge.
   Numbers use tabular figures. */
:root {
  --bg: #eef3f5;
  --paper: #ffffff;
  --ink: #0e1f2b;
  --muted: #475a67;
  --line: #c9d6dd;
  --edge: #8fa3af;
  --console: #10232e;
  --console-ink: #8ff0cf;
  --accent: #0b6a85;
  --accent-soft: #dcecf2;
  --ok: #17663a;
  --ok-soft: #dff1e6;
  --close: #7a5300;
  --close-soft: #f7ecd4;
  --bad: #a2261f;
  --bad-soft: #f8e1de;
  --focus: #1b5fd0;
  --head: "Avenir Next", "Segoe UI", "Helvetica Neue", system-ui, sans-serif;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, "DejaVu Sans Mono", monospace;
  --r: 6px;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b151c;
    --paper: #111f28;
    --ink: #e2edf2;
    --muted: #a2b6c1;
    --line: #26404d;
    --edge: #4c6573;
    --console: #050c11;
    --console-ink: #8ff0cf;
    --accent: #72c8e2;
    --accent-soft: #15303c;
    --ok: #8adca6;
    --ok-soft: #142c1e;
    --close: #f0c56b;
    --close-soft: #352a12;
    --bad: #ff9c8f;
    --bad-soft: #3a1c18;
    --focus: #8ab8ff;
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 17px/1.55 var(--sans); font-variant-numeric: tabular-nums; }
.wrap { max-width: 1120px; margin: 0 auto; padding: 0 16px; }
a { color: var(--accent); text-underline-offset: 2px; }
.skip { position: absolute; left: -999px; top: 8px; background: var(--paper); padding: 8px 12px; z-index: 10; }
.skip:focus { left: 8px; }
:focus-visible { outline: 3px solid var(--focus); outline-offset: 2px; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

.hero { padding: 24px 0 6px; max-width: 760px; }
h1 { font: 700 clamp(1.7rem, 5vw, 2.5rem)/1.1 var(--head); margin: 0 0 8px; letter-spacing: -0.015em; }
.lede { margin: 0 0 4px; color: var(--muted); max-width: 64ch; }
h2 { font: 700 1.3rem/1.25 var(--head); margin: 0 0 10px; }

/* tool: settings beside the sheet on wide screens */
.tool { display: block; }
@media (min-width: 1000px) {
  .tool { display: grid; grid-template-columns: 300px minmax(0, 1fr); gap: 28px; align-items: start; }
}

/* setup */
.setup { margin: 12px 0 6px; }
fieldset { border: 0; padding: 0; margin: 0; min-width: 0; }
legend { font-weight: 700; padding: 0; margin-bottom: 6px; }
.toggles { display: flex; flex-wrap: wrap; gap: 6px; }
@media (min-width: 1000px) { .toggles { display: grid; gap: 4px; } }
.tg { position: relative; display: block; cursor: pointer; }
.tg input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.tg span { display: flex; flex-direction: column; justify-content: center; min-height: 44px; padding: 6px 12px 6px 32px; border: 1px solid var(--line); border-radius: var(--r); background: var(--paper); color: var(--muted); line-height: 1.2; }
.tg span::before { content: ""; position: absolute; left: 11px; top: 50%; width: 12px; height: 12px; margin-top: -6px; border: 2px solid var(--edge); border-radius: 2px; }
.tg b { font-size: 0.95rem; font-weight: 600; }
.tg small { display: none; color: var(--muted); font-size: 0.85rem; }
@media (min-width: 1000px) { .tg small { display: block; } }
.tg input:checked + span { color: var(--ink); border-color: var(--accent); background: var(--accent-soft); }
.tg input:checked + span::before { border-color: var(--accent); background: var(--accent); box-shadow: inset 0 0 0 2px var(--paper); }
.tg input:focus-visible + span { outline: 3px solid var(--focus); outline-offset: 2px; }
.tg .short { display: none; }
.presets { display: flex; gap: 0 14px; flex-wrap: wrap; margin: 2px 0 0; font-size: 15px; }
.setrow { display: flex; align-items: center; gap: 8px 14px; flex-wrap: wrap; margin-top: 4px; }
label.inline { display: flex; align-items: center; gap: 8px; font-weight: 600; }
select, input { font: inherit; font-size: 16px; color: var(--ink); background: var(--paper); border: 1px solid var(--edge); border-radius: var(--r); min-height: 44px; padding: 6px 10px; }
select { max-width: 100%; }
.btn { font: inherit; font-weight: 650; min-height: 44px; padding: 8px 16px; border-radius: var(--r); border: 1px solid var(--ink); background: var(--paper); color: var(--ink); cursor: pointer; }
.btn.primary { background: var(--console); color: var(--console-ink); border-color: var(--console); }
.btn.small { padding: 6px 14px; }
.btn:hover { filter: brightness(0.95); }
.link { font: inherit; background: none; border: 0; padding: 10px 0; min-height: 44px; color: var(--accent); text-decoration: underline; text-underline-offset: 2px; cursor: pointer; }
.rules { margin-top: 10px; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.rules summary { cursor: pointer; padding: 11px 0; font-weight: 700; min-height: 44px; }
.rules summary span { font-weight: 400; color: var(--muted); font-size: 0.92rem; }
.rule-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px 12px; }
.rule-grid label { display: flex; flex-direction: column; gap: 3px; font-size: 0.9rem; font-weight: 600; min-width: 0; }
.rule-grid .wide { grid-column: 1 / -1; }
.hint { color: var(--muted); font-size: 0.9rem; margin: 8px 0 10px; }
.gt { border-collapse: collapse; width: 100%; font-size: 0.88rem; table-layout: fixed; }
.gt th, .gt td { border: 1px solid var(--line); padding: 3px 2px; text-align: center; }
.gt th { font-weight: 600; color: var(--muted); width: 3.6em; text-align: left; padding-left: 4px; }
.gt tr:first-child td { color: var(--muted); font-size: 0.8rem; }
.gt tr:last-child td { font-weight: 700; font-family: var(--mono); }
.gt .na { color: var(--muted); }
.gt input.gc { width: 100%; min-height: 40px; padding: 2px; text-align: center; font-family: var(--mono); border-radius: 3px; }

.note { margin: 12px 0; padding: 10px 12px; border-left: 5px solid var(--close); background: var(--close-soft); }
.note.info { border-left-color: var(--accent); background: var(--accent-soft); }
.note .link { min-height: 0; padding: 0; font-weight: 600; }

/* the sheet: a film with its edge strip */
.sheet { margin: 12px 0 0; background: var(--paper); border: 1px solid var(--line); border-radius: var(--r); overflow: hidden; }
.sheet:focus { outline: none; }
.sheet-head { display: flex; justify-content: space-between; align-items: baseline; gap: 4px 12px; flex-wrap: wrap; background: var(--console); color: #d9e7ee; padding: 9px 16px; }
.sheet-head h2 { margin: 0; color: #fff; font-size: 1.15rem; }
.code { font-family: var(--mono); letter-spacing: 0.08em; color: var(--console-ink); }
.score { margin: 0; font-family: var(--mono); font-size: 0.92rem; }
.practice { margin: 0; padding: 7px 16px; font-size: 0.92rem; color: var(--muted); border-bottom: 1px solid var(--line); }
.probs { list-style: none; margin: 0; padding: 0; }
.prob { display: grid; grid-template-columns: 44px minmax(0, 1fr); border-bottom: 1px solid var(--line); }
.num { background: var(--console); color: var(--console-ink); font: 700 0.95rem var(--mono); text-align: center; padding-top: 16px; border-right: 3px solid var(--edge); }
.pbody { padding: 12px 16px 6px; min-width: 0; }
.tag { margin: 0; font-size: 0.85rem; color: var(--accent); font-weight: 600; }
.q { margin: 3px 0 8px; max-width: 68ch; }
.q .rt { color: var(--muted); font-size: 0.92rem; }
.arow { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; }
.ain { display: inline-flex; align-items: center; gap: 6px; }
.ain input { width: 8.5em; font-family: var(--mono); }
.ain .unit { color: var(--muted); font-size: 0.95rem; min-width: 2.2em; }
.fbwrap:empty { display: none; }
.fb { margin: 8px 0 0; padding: 6px 10px; display: inline-block; max-width: 100%; border-radius: 4px; }
.fb.right { background: var(--ok-soft); color: var(--ok); }
.fb.close { background: var(--close-soft); color: var(--close); }
.fb.wrong, .fb.unread { background: var(--bad-soft); color: var(--bad); }
.prob.is-right .ain input { border-color: var(--ok); box-shadow: inset 0 0 0 1px var(--ok); }
.prob.is-close .ain input { border-color: var(--close); box-shadow: inset 0 0 0 1px var(--close); }
.prob.is-wrong .ain input { border-color: var(--bad); box-shadow: inset 0 0 0 1px var(--bad); }
.prob.is-right .num { color: #b8ffd0; }
.work { margin-top: 2px; }
.work > summary { cursor: pointer; color: var(--muted); font-size: 0.92rem; padding: 10px 0; min-height: 44px; display: flex; align-items: center; list-style: none; }
.work > summary::-webkit-details-marker { display: none; }
.work > summary::before { content: "+"; margin-right: 6px; font-weight: 700; font-family: var(--mono); }
.work[open] > summary::before { content: "−"; }
.ans { margin: 0 0 6px; }
.steps { margin: 4px 0 8px; padding-left: 1.6em; font-size: 0.93rem; line-height: 1.55; overflow-wrap: anywhere; }
.sheet-foot { display: flex; align-items: center; gap: 16px; flex-wrap: wrap; padding: 10px 16px 12px; }

.share { margin: 16px 0 8px; }
.print-row { display: flex; align-items: flex-end; gap: 8px 10px; flex-wrap: wrap; }
.print-row label { display: flex; flex-direction: column; gap: 3px; font-size: 0.9rem; font-weight: 600; }
.share-out label { display: flex; flex-direction: column; gap: 3px; font-size: 0.9rem; font-weight: 600; }
.share-out input { width: 100%; font-size: 16px; }
.recent { margin-top: 12px; border-top: 1px solid var(--line); }
.recent summary { cursor: pointer; padding: 11px 0; font-weight: 600; min-height: 44px; }
.recent ul { list-style: none; margin: 0; padding: 0; }
.recent li { display: flex; justify-content: space-between; align-items: center; gap: 10px; border-top: 1px solid var(--line); padding: 4px 0; }
.recent small { display: block; color: var(--muted); }

.toast { position: fixed; left: 50%; bottom: 16px; transform: translate(-50%, 160%); background: var(--console); color: #e6f3f7; padding: 10px 14px; border-radius: var(--r); max-width: calc(100% - 32px); transition: transform 0.2s; z-index: 20; }
.toast.on { transform: translate(-50%, 0); }
@media (prefers-reduced-motion: reduce) { .toast { transition: none; } }

/* content */
.content { padding: 22px 0 8px; max-width: 820px; }
.content h2 { margin-top: 30px; }
.content p { max-width: 68ch; }
.worked { max-width: 66ch; padding-left: 1.4em; }
.worked li { margin: 2px 0; }
.tablewrap { overflow-x: auto; }
table.src { border-collapse: collapse; width: 100%; font-size: 0.9rem; }
.src th, .src td { text-align: left; vertical-align: top; padding: 7px 8px 7px 0; border-bottom: 1px solid var(--line); }
.src th { border-bottom: 2px solid var(--ink); font-size: 0.85rem; color: var(--muted); }
.checked { color: var(--muted); font-size: 0.92rem; }
.faq details { border-bottom: 1px solid var(--line); }
.faq summary { cursor: pointer; padding: 11px 0; font-weight: 600; min-height: 44px; }
.faq details p { margin: 0 0 12px; }
.sources { font-size: 0.9rem; color: var(--muted); overflow-wrap: anywhere; margin-top: 22px; }

footer { border-top: 1px solid var(--line); margin-top: 20px; padding: 16px 0 28px; color: var(--muted); font-size: 0.92rem; }
.indep { margin: 0 0 10px; }
.sb-footer p { margin: 6px 0; }
.sb-more { line-height: 1.8; }
.sb-footer a { color: var(--ink); }

@media (max-width: 600px) {
  .hero { padding-top: 14px; }
  .toggles { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 5px; }
  .tg .long { display: none; }
  .tg .short { display: block; }
  .tg span { padding: 6px 4px; text-align: center; align-items: center; }
  .tg span::before { display: none; }
  .tg input:checked + span { background: var(--console); color: var(--console-ink); border-color: var(--console); }
  /* dark: the console fill is darker than an unticked box, so "on" needs its own edge to not read as "off" */
  @media (prefers-color-scheme: dark) { .tg input:checked + span { border-color: var(--console-ink); } }
  .presets { gap: 0 12px; }
  .sheet { margin-left: -16px; margin-right: -16px; border-left: 0; border-right: 0; border-radius: 0; }
  .prob { grid-template-columns: 34px minmax(0, 1fr); }
  .num { font-size: 0.85rem; }
  .pbody { padding: 10px 12px 4px; }
}
@media (max-width: 480px) {
  body { font-size: 16.5px; }
  .ain input { width: 7.5em; }
  .rule-grid { grid-template-columns: 1fr; }
  .src td:nth-child(2) { min-width: 8em; }
}

/* print: only the worksheet and key */
.print-root { display: none; }
@page { margin: 0.55in 0.6in; }
@media print {
  :root { --ink: #000; --muted: #333; --line: #999; --paper: #fff; }
  body { background: #fff; color: #000; font: 10.5pt/1.38 var(--sans); }
  main, footer, .toast, .skip { display: none !important; }
  .print-root { display: block; }
  table.pt { width: 100%; border-collapse: collapse; }
  table.pt > tbody > tr > td, table.pt > thead > tr > td { padding: 0; }
  .prun { font: 8.5pt var(--sans); color: #555; text-align: right; padding-bottom: 6pt !important; }
  .ph { display: flex; justify-content: space-between; align-items: baseline; border-bottom: 2pt solid #000; margin-bottom: 7pt; }
  .ph h2 { font: 700 15pt var(--head); margin: 0; }
  .ph p { margin: 0; font: 10.5pt var(--sans); }
  .pmeta { display: flex; justify-content: space-between; gap: 12pt; margin: 4pt 0 8pt; }
  .plabel { margin: 0 0 5pt; font-size: 9pt; font-style: italic; }
  .pconv { border: 0.75pt solid #000; border-left: 4pt solid #000; padding: 4pt 8pt; margin: 0 0 5pt; font-size: 9pt; break-inside: avoid; page-break-inside: avoid; }
  .pconv ul, .pform ul { margin: 2pt 0 0; padding-left: 12pt; }
  .pform { border: 0.75pt solid #000; padding: 4pt 8pt; margin: 0 0 6pt; font-size: 9pt; break-inside: avoid; page-break-inside: avoid; }
  .pq { margin: 0; padding-left: 20pt; }
  .pq > li { break-inside: avoid; page-break-inside: avoid; padding: 5pt 0 6pt; border-bottom: 0.75pt solid #999; }
  .pq > li p { margin: 0; }
  .prt { font-size: 9pt; color: #333; }
  .pans { margin-top: 0.55in !important; text-align: right; }
  .psheet + .pkey { break-before: page; page-break-before: always; }
  .pk { margin: 0; padding-left: 20pt; }
  .pk > li { break-inside: avoid; page-break-inside: avoid; padding: 4pt 0 5pt; border-bottom: 0.75pt solid #bbb; }
  .pk p { margin: 0; }
  .pkq { font-size: 9pt; color: #333; }
  .pka { font: 700 11pt var(--sans); margin-top: 2pt !important; }
  .pks { margin: 1pt 0 0; padding-left: 14pt; font-size: 9pt; line-height: 1.35; }
}
.nf-box { margin: 12px 0; max-width: 62ch; color: var(--muted); }
a.btn { display: inline-flex; align-items: center; text-decoration: none; }