/* Ticker Tape Practice: a physics bench. Cool grey bench, cream paper tape with carbon-black dots, a steel ruler,
   a slab-serif heading face and the orange of a timer's warning label. On paper: black on white, tapes at full size. */
:root {
  --bg: #eef1f3;
  --paper: #ffffff;
  --ink: #1a1f24;
  --muted: #4a535c;
  --line: #d2d8dd;
  --edge: #87919a;
  --accent: #b2430e;
  --accent-ink: #ffffff;
  --accent-soft: #fbe6da;
  --info: #1d5d78;
  --ok: #17663a;
  --ok-soft: #dff1e6;
  --close: #7a5300;
  --close-soft: #f7ecd4;
  --bad: #a2261f;
  --bad-soft: #f8e1de;
  --focus: #1b5fd0;
  --tape: #fbf5df;
  --tape-edge: #c9bd97;
  --dot: #17171a;
  --rule: #e9edf0;
  --rule-edge: #8f9aa3;
  --bench: #dfe5e9;
  --head: Rockwell, "Rockwell Nova", "Roboto Slab", "Zilla Slab", "DejaVu Serif", Georgia, 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: 3px;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #11161b;
    --paper: #1a2128;
    --ink: #e5e9ec;
    --muted: #a6b0b9;
    --line: #2d363f;
    --edge: #5e6973;
    --accent: #ff9d66;
    --accent-ink: #2b1205;
    --accent-soft: #3a2014;
    --info: #7cc7e6;
    --ok: #8adca6;
    --ok-soft: #142c1e;
    --close: #f0c56b;
    --close-soft: #352a12;
    --bad: #ff9c8f;
    --bad-soft: #3a1c18;
    --focus: #8ab8ff;
    --bench: #232c35;
  }
}
* { 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); }
.wrap { max-width: 1180px; 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; }

.hero { padding: 20px 0 0; max-width: 820px; }
h1 { font: 700 clamp(1.9rem, 5.4vw, 2.9rem)/1.05 var(--head); margin: 0 0 6px; letter-spacing: -0.01em; }
.lede { margin: 0; color: var(--muted); max-width: 66ch; }
.hero-tape { display: block; width: 100%; max-width: 820px; height: 22px; margin: 12px 0 0; }
.hero-tape .ht { fill: var(--tape); stroke: var(--tape-edge); stroke-width: 1; }
.hero-tape .hd { fill: var(--dot); }
h2 { font: 700 1.35rem/1.2 var(--head); margin: 0 0 10px; }

/* layout: settings across the top with the facts card beside them on wide screens, the sheet at full width below */
.tool { display: flex; flex-direction: column; }
.setup { order: 1; margin: 14px 0 4px; }
.work-area { order: 2; min-width: 0; }
.facts { order: 3; }
@media (min-width: 1020px) {
  .tool { display: grid; grid-template-columns: minmax(0, 1fr) 330px; column-gap: 40px; align-items: start; }
  .setup { grid-column: 1; grid-row: 1; margin-top: 18px; }
  .facts { grid-column: 2; grid-row: 1; margin-top: 18px; }
  .work-area { grid-column: 1 / -1; grid-row: 2; }
}
fieldset { border: 0; padding: 0; margin: 0 0 10px; min-width: 0; }
legend { font-weight: 700; padding: 0; margin-bottom: 6px; }
.toggles { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); gap: 6px; }
.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; height: 100%; padding: 6px 10px 6px 12px; border: 1px solid var(--line); border-left: 4px solid var(--line); border-radius: var(--r); background: var(--paper); color: var(--muted); line-height: 1.2; }
.tg b { font-size: 0.95rem; font-weight: 650; }
.tg small { display: none; color: var(--muted); font-size: 0.84rem; margin-top: 2px; }
@media (min-width: 1100px) { .tg small { display: block; } }
.tg input:checked + span { color: var(--ink); border-color: var(--edge); border-left-color: var(--accent); background: var(--paper); }
.tg input:not(:checked) + span { background: transparent; text-decoration: line-through; text-decoration-color: var(--edge); }
.tg input:focus-visible + span, .sg input:focus-visible + span, .check input:focus-visible + span { outline: 3px solid var(--focus); outline-offset: 2px; }
.tg .short { display: none; }
.opts-row { display: flex; flex-wrap: wrap; gap: 4px 18px; }
.opts-row fieldset { flex: 0 1 auto; }
.seg { display: inline-grid; grid-auto-flow: column; grid-auto-columns: minmax(84px, auto); border: 1px solid var(--edge); border-radius: var(--r); overflow: hidden; background: var(--paper); }
.sg { position: relative; display: block; cursor: pointer; }
.sg + .sg { border-left: 1px solid var(--edge); }
.sg input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.sg > span { display: flex; align-items: center; justify-content: center; min-height: 44px; padding: 4px 12px; text-align: center; font-size: 0.93rem; font-weight: 600; line-height: 1.15; white-space: nowrap; }
.sg input:checked + span { background: var(--ink); color: var(--bg); }
.check { position: relative; display: flex; align-items: center; gap: 10px; min-height: 44px; margin: 0 0 6px; cursor: pointer; font-size: 0.95rem; }
.check input { width: 20px; height: 20px; min-height: 0; margin: 0; accent-color: var(--accent); flex: none; }
.setrow { display: flex; align-items: center; gap: 8px 14px; flex-wrap: wrap; }
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(--accent); color: var(--accent-ink); border-color: var(--accent); }
.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; }

/* the facts card: the answer to "time between dots" on the first screen */
.facts { margin: 16px 0 6px; padding: 12px 14px 8px; background: var(--bench); border-radius: var(--r); font-size: 0.95rem; max-width: 520px; }
.facts h2 { font-size: 1.12rem; margin: 0 0 6px; }
.facts dl { margin: 0; }
.facts dl div { display: grid; grid-template-columns: 9.5em 1fr; gap: 8px; padding: 5px 0; border-top: 1px solid var(--line); }
.facts dt { color: var(--muted); }
.facts dd { margin: 0; font-weight: 600; }

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

/* the sheet */
.sheet { margin: 12px 0 0; }
.sheet:focus { outline: none; }
.sheet-head { display: flex; justify-content: space-between; align-items: baseline; gap: 4px 12px; flex-wrap: wrap; border-bottom: 3px solid var(--ink); padding-bottom: 4px; }
.sheet-head h2 { margin: 0; font-size: 1.3rem; }
.code { font-family: var(--mono); letter-spacing: 0.08em; color: var(--accent); }
.score { margin: 0; font-size: 0.95rem; color: var(--muted); }
.practice { margin: 6px 0 0; font-size: 0.93rem; color: var(--muted); }
.qs { list-style: none; margin: 0; padding: 0; }
.q { border-bottom: 1px solid var(--line); padding: 20px 0 10px; }
.q h3 { font: 700 1.2rem/1.25 var(--head); margin: 0 0 4px; }
.q h3 .qn { color: var(--accent); margin-right: 8px; }
.q .scen { margin: 0 0 10px; max-width: 72ch; }

/* the tape */
.figwrap { position: relative; margin: 0 0 14px; }
.tf { margin: 0; padding: 10px 10px 6px; background: var(--bench); border-radius: var(--r); max-width: 940px; }
.tapeview { overflow: hidden; }
.tapeview svg { display: block; width: 100%; height: auto; }
.qs.zoomed .tapeview { overflow-x: auto; overscroll-behavior-x: contain; }
.qs.zoomed .tapeview svg { width: 1040px; max-width: none; }
.figwrap .zoom { margin: 0 0 6px; }
.slide-hint { display: none; margin: 4px 0 0; font-size: 0.85rem; color: var(--muted); }
.qs.zoomed .slide-hint { display: block; }
@media (min-width: 900px) { .figwrap .zoom, .qs.zoomed .slide-hint { display: none; } .qs.zoomed .tapeview svg { width: 100%; } .qs.zoomed .tapeview { overflow: hidden; } }
.tf figcaption { font-size: 0.88rem; color: var(--muted); margin-top: 4px; }
.tape-svg .tape { fill: var(--tape); stroke: var(--tape-edge); stroke-width: 0.25; }
.tape-svg .dot { fill: var(--dot); }
.tape-svg .cut { fill: none; stroke: #8d7f5a; stroke-width: 0.25; stroke-dasharray: 0.8 0.6; }
.tape-svg .rb { fill: var(--rule); stroke: var(--rule-edge); stroke-width: 0.2; }
.tape-svg .tk { fill: none; stroke: #1a1f24; stroke-width: 0.13; }
.tape-svg .rn, .tape-svg .ru { font: 2.4px var(--sans); fill: #1a1f24; text-anchor: middle; }
.tape-svg .ru { text-anchor: start; font-size: 2px; }
.tape-svg .dn { font: 600 2.3px var(--sans); fill: #5b4d23; text-anchor: middle; }
.tape-svg .pl, .tape-svg .bl, .tape-svg .sn, .tape-svg .wl { font: 700 2.6px var(--sans); fill: var(--ink); text-anchor: middle; }
.tape-svg .sn { font-weight: 600; fill: var(--muted); font-size: 2.3px; }
.tape-svg .wl { font-weight: 600; font-size: 2.3px; }
.tape-svg .pt, .tape-svg .br { fill: none; stroke: var(--accent); stroke-width: 0.3; }

/* the tape chart */
.chart-svg { display: block; width: 100%; max-width: 380px; height: auto; }
.chart-svg .cs { fill: var(--tape); stroke: var(--tape-edge); stroke-width: 0.3; }
.chart-svg.live .cs { fill: var(--accent-soft); stroke: var(--accent); }
.chart-svg .cd { fill: var(--dot); }
.chart-svg .cg { stroke: var(--line); stroke-width: 0.25; }
.chart-svg .cg2 { stroke: var(--line); stroke-width: 0.15; }
.chart-svg .cax { fill: none; stroke: var(--ink); stroke-width: 0.35; }
.chart-svg .cl { fill: none; stroke: var(--accent); stroke-width: 0.4; stroke-dasharray: 1.2 0.8; }
.chart-svg .ca, .chart-svg .cx, .chart-svg .ct { font: 2.6px var(--sans); fill: var(--muted); }
.chart-svg .ca { text-anchor: end; }
.chart-svg .cx, .chart-svg .ct { text-anchor: middle; }
.kchart { margin: 6px 0 10px; }

/* questions */
.qparts { max-width: 780px; }
.part { margin: 0 0 14px; min-width: 0; }
.part > .prompt, .part legend { display: block; font-weight: 600; margin: 0 0 6px; }
.opts { display: grid; gap: 4px; }
.opt { position: relative; display: flex; gap: 10px; align-items: flex-start; min-height: 44px; padding: 9px 10px; border: 1px solid var(--line); border-radius: var(--r); background: var(--paper); cursor: pointer; }
.opt input { margin: 3px 0 0; min-height: 0; width: 18px; height: 18px; accent-color: var(--accent); flex: none; }
.opt .ot { min-width: 0; }
.opt:has(input:checked) { border-color: var(--accent); box-shadow: inset 3px 0 0 var(--accent); }
.ain { display: inline-flex; align-items: center; gap: 6px; max-width: 100%; }
.ain input { width: 9em; font-family: var(--mono); }
.ain .unit { color: var(--muted); }
.mgrid { display: flex; flex-wrap: wrap; gap: 8px 10px; }
.mi { display: flex; flex-direction: column; gap: 2px; font-size: 0.86rem; color: var(--muted); }
.mi input { width: 5.2em; font-family: var(--mono); }
.mi.is-right input { border-color: var(--ok); box-shadow: inset 0 0 0 1px var(--ok); }
.mi.is-wrong input, .mi.is-unread input { border-color: var(--bad); box-shadow: inset 0 0 0 1px var(--bad); }
.mi.is-close input { border-color: var(--close); box-shadow: inset 0 0 0 1px var(--close); }
.live { margin: 10px 0 0; }
.live .hint { margin: 0; }
.qfoot { display: flex; align-items: center; gap: 4px 16px; flex-wrap: wrap; }
.fbwrap:empty { display: none; }
.fb { margin: 6px 0 0; padding: 6px 10px; border-radius: var(--r); max-width: 70ch; }
.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); }
.part.is-right .ain input { border-color: var(--ok); box-shadow: inset 0 0 0 1px var(--ok); }
.part.is-wrong .ain input, .part.is-unread .ain input { border-color: var(--bad); box-shadow: inset 0 0 0 1px var(--bad); }
.part.is-close .ain input { border-color: var(--close); box-shadow: inset 0 0 0 1px var(--close); }
.work { margin-top: 4px; }
.work > summary { cursor: pointer; color: var(--muted); font-size: 0.93rem; 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: "−"; }
.work .ans { margin: 0 0 2px; }
.steps { margin: 2px 0 10px; padding-left: 1.4em; font-size: 0.94rem; overflow-wrap: anywhere; }
.sheet-foot { display: flex; align-items: center; gap: 16px; flex-wrap: wrap; padding: 12px 0; }

.share { margin: 10px 0 8px; }
.print-row { display: flex; align-items: flex-end; gap: 8px 10px; flex-wrap: wrap; }
.print-row label, .share-out label { display: flex; flex-direction: column; gap: 3px; font-size: 0.9rem; font-weight: 600; }
.share-out input { width: 100%; }
.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); }
.hint { color: var(--muted); font-size: 0.9rem; margin: 8px 0 10px; }

.toast { position: fixed; left: 50%; bottom: 16px; transform: translate(-50%, 160%); background: var(--ink); color: var(--bg); 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; }
.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: 0.92rem; 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); }
a.btn { display: inline-flex; align-items: center; text-decoration: none; }

@media (max-width: 760px) {
  .hero { padding-top: 8px; }
  .toggles { gap: 5px; }
  .tg .long { display: none; }
  .tg .short { display: block; }
  .tg span { padding: 5px 2px; text-align: center; align-items: center; font-size: 0.9rem; border-left-width: 1px; }
  .tg input:checked + span { background: var(--ink); color: var(--bg); border-color: var(--ink); }
  .tg input:not(:checked) + span { text-decoration: none; }
  .opts-row { gap: 0 12px; }
  .seg { grid-auto-columns: minmax(64px, auto); }
  .sg > span { padding: 4px 8px; font-size: 0.9rem; }
  .tf { padding: 8px 6px 4px; margin: 0 -6px; }
}

/* print: worksheet and key only; tapes at full size, black on white */
.print-root { display: none; }
@page { margin: 0.45in 0.5in; }
@media print {
  :root { --ink: #000; --muted: #333; --line: #999; --paper: #fff; --edge: #555; --tape: #fff; --tape-edge: #000; --dot: #000; --rule: #fff; --rule-edge: #000; --accent: #000; --accent-soft: #fff; }
  body { background: #fff; color: #000; font: 10.5pt/1.38 var(--sans); }
  main, footer, .toast, .skip { display: none !important; }
  .print-root { display: block; }
  svg { print-color-adjust: exact; -webkit-print-color-adjust: exact; }
  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: #444; text-align: right; padding-bottom: 6pt !important; }
  .ph { display: flex; justify-content: space-between; align-items: baseline; border-bottom: 2pt solid #000; margin-bottom: 6pt; }
  .ph h2 { font: 700 15pt var(--head); margin: 0; }
  .ph p { margin: 0; }
  .pmeta { display: flex; justify-content: space-between; gap: 12pt; margin: 4pt 0 6pt; }
  .pbar { display: flex; align-items: center; gap: 4mm; margin: 0 0 4pt; font-size: 9pt; }
  .checkbar { width: 104mm; height: 9mm; flex: none; }
  .checkbar .cbb { stroke: #000; stroke-width: 0.5; }
  .checkbar .cbt { stroke: #000; stroke-width: 0.35; }
  .plabel { margin: 0 0 6pt; font-size: 9pt; font-style: italic; }
  .pq { list-style: none; margin: 0; padding: 0; }
  .pq > li { padding: 6pt 0 4pt; border-bottom: 0.75pt solid #999; break-inside: avoid; page-break-inside: avoid; }
  /* every question stays whole when it fits a page (Chrome still breaks one taller than a page, between its tape and
     its parts, which then start with "Question 4, parts a to d"). The first question may break after its tape, so a tall
     first question never leaves page 1 empty under the sheet header. */
  .pq > li.pq-tall:first-child { break-inside: auto; page-break-inside: auto; }
  .pcont { margin: 2pt 0 3pt !important; font: italic 8.5pt var(--sans); color: #444; break-after: avoid; page-break-after: avoid; }
  .pq > li.pq-tall .pparts { break-inside: avoid; page-break-inside: avoid; } /* the parts move as one block behind their title line */

  .pqtop { break-inside: avoid; page-break-inside: avoid; } /* heading, text and tape stay together */
  .pq h3 { font: 700 11.5pt var(--head); margin: 0 0 2pt; }
  .pq .pscen { margin: 0 0 4pt; }
  .pq .tf { padding: 0; background: none; margin: 0 0 4pt; max-width: none; break-inside: avoid; page-break-inside: avoid; }
  .pq .tapeview { overflow: visible; }
  .pq .tapeview svg.tape-svg { width: 180mm; height: auto; max-width: none; }
  .pq .tf figcaption { font-size: 8.5pt; color: #000; }
  .tape-svg .tape { stroke-width: 0.25; }
  .tape-svg .cut { stroke: #000; }
  .tape-svg .tk { stroke: #000; stroke-width: 0.12; }
  .tape-svg .rn, .tape-svg .ru, .tape-svg .dn, .tape-svg .pl, .tape-svg .bl, .tape-svg .sn, .tape-svg .wl { fill: #000; }
  .tape-svg .pt, .tape-svg .br { stroke: #000; }
  .noruler .tape-svg .ruler { display: none; }
  .pparts { display: grid; grid-template-columns: 1fr 1fr; column-gap: 8mm; align-items: start; }
  .pparts .pp { margin: 0 0 8pt; break-inside: avoid; page-break-inside: avoid; }
  .pparts .pp.wide { grid-column: 1 / -1; display: grid; grid-template-columns: auto 1fr; column-gap: 8mm; align-items: start; }
  .pparts .pp.wide > p:first-child { grid-column: 1 / -1; }
  .pparts .pp.wide .pgrid-cap { display: none; }
  .pparts .pp p { margin: 0 0 3pt; }
  .pparts ol.popts { margin: 0; padding-left: 15pt; list-style: upper-alpha; }
  .pparts ol.popts li { margin: 0 0 2pt; }
  .pparts .pline { margin-top: 12pt !important; }
  .pstrips { border-collapse: collapse; margin: 2pt 0 6pt; font-size: 9pt; }
  .pstrips th, .pstrips td { border: 0.6pt solid #000; padding: 3pt 6pt; min-width: 13mm; height: 7mm; text-align: center; }
  .pstrips th { text-align: left; font-weight: 600; }
  .pgrid-cap { margin: 0 0 2pt !important; font-size: 9pt; }
  .chart-svg { width: 92mm; max-width: none; }
  .chart-svg.blank { width: 72mm; }
  .chart-svg .cs { fill: #fff; stroke: #000; }
  .chart-svg .cd { fill: #000; }
  .chart-svg .cg { stroke: #888; stroke-width: 0.2; }
  .chart-svg .cg2 { stroke: #bbb; stroke-width: 0.12; }
  .chart-svg .cax { stroke: #000; }
  .chart-svg .cl { stroke: #000; }
  .chart-svg .ca, .chart-svg .cx, .chart-svg .ct { fill: #000; }
  .pkey { break-before: page; page-break-before: always; }
  .pk { margin: 0; padding-left: 18pt; }
  .pk > li { padding: 4pt 0 5pt; border-bottom: 0.75pt solid #bbb; break-inside: avoid; page-break-inside: avoid; }
  .pk .pkp { break-inside: avoid; page-break-inside: avoid; }
  .pk h3 { font: 700 10.5pt var(--head); margin: 0; break-after: avoid; page-break-after: avoid; }
  .pk p { margin: 1pt 0 0; }
  .pk .pka { font-weight: 700; }
  .pk ul { margin: 1pt 0 0; padding-left: 13pt; font-size: 9pt; line-height: 1.35; }
  .pk .kchart { break-inside: avoid; page-break-inside: avoid; }
  .pk .kchart .chart-svg { width: 80mm; }
}