/* Multimeter Reading Practice: a bench meter. Charcoal case edges, a cream dial face with black ink that stays light
   in dark mode (as a real meter does), a silver mirror band, and test-lead red as the one accent. Geometric headings
   like the lettering on an instrument panel. Black on white on paper, every scale readable without colour. */
:root {
  --bg: #f1f1ee;
  --paper: #ffffff;
  --ink: #17191b;
  --muted: #4e5459;
  --line: #d3d5d3;
  --edge: #6f767b;
  --case: #26292c;
  --accent: #b3261e;
  --accent-ink: #ffffff;
  --accent-soft: #f7e1de;
  --info: #1f5f8b;
  --ok: #17663a;
  --ok-soft: #dcefe2;
  --close: #7a5200;
  --close-soft: #f6ecd3;
  --bad: #a3241d;
  --bad-soft: #f8e0dd;
  --focus: #1b5fd0;
  --face: #fbfaf5;
  --face-ink: #111214;
  --mirror: #dde1e4;
  --head: "Avenir Next", Avenir, "Century Gothic", Futura, "Trebuchet MS", 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: #141516;
    --paper: #1d1f21;
    --ink: #e7e9ea;
    --muted: #a9b0b5;
    --line: #33373a;
    --edge: #6b7378;
    --case: #0b0c0d;
    --accent: #ff8a7a;
    --accent-ink: #2a0703;
    --accent-soft: #3c1d19;
    --info: #8cc4ef;
    --ok: #8adca6;
    --ok-soft: #14301f;
    --close: #f0c56b;
    --close-soft: #352a12;
    --bad: #ff9c8f;
    --bad-soft: #3a1c18;
    --focus: #8ab8ff;
  }
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 17px/1.55 var(--sans); }
.wrap { max-width: 1120px; margin: 0 auto; padding: 0 16px; }
a { color: var(--info); text-underline-offset: 2px; }
.skip { position: absolute; left: -999px; top: 8px; background: var(--paper); padding: 8px 12px; z-index: 10; }
.skip:focus { left: 8px; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
:focus-visible { outline: 3px solid var(--focus); outline-offset: 2px; }
h1, h2, h3 { font-family: var(--head); font-weight: 600; line-height: 1.15; letter-spacing: -0.005em; }
.hero { padding: 20px 0 10px; }
.hero h1 { font-size: clamp(29px, 5.6vw, 44px); margin: 0 0 6px; }
.lede { margin: 0; max-width: 64ch; color: var(--muted); }
.crumb { margin: 12px 0 0; font-size: 15px; }

/* ---------- controls ---------- */
.setup { background: var(--paper); border: 1px solid var(--line); border-top: 5px solid var(--case); border-radius: var(--r); padding: 12px 14px; }
.setgrid { display: grid; grid-template-columns: 1fr auto auto; gap: 10px 14px; align-items: end; }
fieldset { border: 0; margin: 0; padding: 0; min-width: 0; }
legend { font: 600 14px var(--sans); color: var(--muted); padding: 0; margin-bottom: 4px; }
.seg { display: grid; border: 1px solid var(--edge); border-radius: var(--r); overflow: hidden; }
.seg2 { grid-template-columns: 1fr 1fr; }
.seg3 { grid-template-columns: 1fr 1fr 1fr; }
.sg { position: relative; display: block; min-width: 0; }
.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; text-align: center; min-height: 44px; padding: 4px 6px; font-size: 15px; line-height: 1.15; }
.sg input:checked + span { background: var(--case); color: #fff; font-weight: 600; }
@media (prefers-color-scheme: dark) { .sg input:checked + span { background: var(--ink); color: var(--bg); } }
.sg input:focus-visible + span { outline: 3px solid var(--focus); outline-offset: -3px; }
.tdet { margin-top: 6px; }
.tdet summary { cursor: pointer; font-weight: 600; min-height: 44px; display: flex; align-items: center; gap: 6px; }
.tsum { font-weight: 400; color: var(--muted); font-size: 15px; }
.toggles { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 6px; padding-top: 4px; }
.tg { display: flex; gap: 8px; align-items: flex-start; padding: 8px; border: 1px solid var(--line); border-radius: var(--r); cursor: pointer; min-height: 44px; }
.tg input { width: 20px; height: 20px; margin: 2px 0 0; accent-color: var(--accent); flex: none; }
.tg b { display: block; font-weight: 600; font-size: 15.5px; }
.tg small { display: block; color: var(--muted); font-size: 14px; line-height: 1.3; }
.tg.off { opacity: 0.55; }
.inline { display: inline-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; }
.btn { font: 600 16px var(--sans); min-height: 44px; padding: 8px 16px; border-radius: var(--r); border: 1px solid var(--edge); background: var(--paper); color: var(--ink); cursor: pointer; }
.btn:hover { border-color: var(--ink); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn.small { min-height: 40px; padding: 6px 12px; font-size: 15px; }
.link { font: inherit; background: none; border: 0; color: var(--info); text-decoration: underline; text-underline-offset: 2px; cursor: pointer; min-height: 44px; padding: 0 4px; }

/* ---------- the sheet ---------- */
.work-area { margin-top: 14px; }
.note { margin: 0 0 10px; padding: 10px 12px; border-left: 4px solid var(--bad); background: var(--bad-soft); border-radius: var(--r); font-size: 15.5px; }
.note.info { border-color: var(--info); background: var(--paper); }
.sheet:focus { outline: none; }
.sheet-head { display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between; gap: 4px 14px; }
.sheet-head h2 { font-size: 25px; margin: 4px 0 0; }
.code { font-family: var(--mono); letter-spacing: 0.06em; }
.score { margin: 0; color: var(--muted); font-size: 15px; }
.sline { margin: 2px 0 8px; color: var(--muted); font-size: 14.5px; }
.qs { list-style: none; margin: 0; padding: 0; display: grid; gap: 14px; }
.q { background: var(--paper); border: 1px solid var(--line); border-left: 5px solid var(--case); border-radius: var(--r); padding: 12px 14px 14px; min-width: 0; }
@media (prefers-color-scheme: dark) { .q { border-left-color: var(--edge); } .setup { border-top-color: var(--edge); } }
.q h3 { font-size: 20px; margin: 0; }
.qhead { display: flex; justify-content: space-between; align-items: center; gap: 10px; }
.zoom { display: none; min-height: 40px; padding: 4px 12px; white-space: nowrap; }
.figview { min-width: 0; }
.qn { color: var(--accent); margin-right: 6px; }
.scen { margin: 4px 0 8px; max-width: 70ch; }
.qbody { display: grid; grid-template-columns: minmax(0, 1fr); gap: 10px 22px; }
.meter { display: flex; flex-wrap: wrap; gap: 8px 14px; align-items: flex-end; }
.dialfig, .knobfig { margin: 0; min-width: 0; }
.dialfig { flex: 3 1 340px; max-width: 560px; }
.meter.two .dialfig { flex-basis: 240px; max-width: 420px; }
.knobfig { flex: 1 1 150px; max-width: 210px; }
.meter.knobonly .knobfig { flex: 0 0 220px; }
.dialfig figcaption { font-size: 14.5px; font-weight: 600; color: var(--muted); margin-bottom: 2px; }
svg.fig { display: block; width: 100%; height: auto; }

/* drawing ink: the dial face stays light in both themes, like a real meter */
.win { fill: var(--face); stroke: var(--case); stroke-width: 3; }
@media (prefers-color-scheme: dark) { .win { stroke: #52585c; } }
.mirror { fill: var(--mirror); stroke: #8d969b; stroke-width: 0.8; }
.sc { fill: none; stroke: var(--face-ink); stroke-width: 1.3; }
.tk { stroke: var(--face-ink); stroke-width: 1; }
.tk.mj { stroke-width: 1.7; }
.fig text, svg .fig { fill: var(--face-ink); }
svg text { fill: var(--face-ink); font-family: var(--sans); }
.fig.ohm { font-size: 18px; }
.fig.inf { font-size: 21px; }
.fig.r10, .fig.r50, .fig.r250 { font-size: 17px; }
.fig.p0 { font-size: 18px; }
.fig.p1 { font-size: 16px; }
.fig.use { font-weight: 700; fill: var(--accent); }
@media (prefers-color-scheme: dark) { .fig.use, .kl.use { fill: #b3261e; } }
.nm { font-size: 14px; font-style: italic; }
.dnote { font-size: 14px; fill: #3b4045 !important; }
.unit { font: 700 34px var(--head); }
.ndl path { stroke: var(--face-ink); stroke-width: 2.4; stroke-linecap: round; }
.rfl path { stroke: #5d6468; stroke-width: 1.8; }
.tru path { stroke: #b3261e; stroke-width: 1.6; stroke-dasharray: 5 4; }
.kring { fill: var(--face); stroke: var(--case); stroke-width: 1.5; }
.ktk { stroke: var(--face-ink); stroke-width: 1.4; }
.ksep { stroke: #8d969b; stroke-width: 1.2; stroke-dasharray: 3 3; }
.kbody { fill: #2b2e31; stroke: #0d0e0f; stroke-width: 1.5; }
.kp path { stroke: #f4f4f0; stroke-width: 5; stroke-linecap: round; }
.kp .kptip { fill: #f4f4f0; stroke: none; }
.kl { font-size: 19px; }
.kl.use { font-weight: 700; fill: var(--accent); }
.kg { font: 700 19px var(--head); }
svg.knob { background: none; }

/* answer boxes */
.qparts { display: grid; grid-template-columns: 1fr; gap: 10px; margin-top: 4px; align-content: start; }
.part { border: 0; margin: 0; padding: 0; min-width: 0; }
.part .prompt, .part legend { display: block; font-weight: 600; font-size: 16px; line-height: 1.3; margin-bottom: 4px; color: var(--ink); }
.ain { display: flex; align-items: center; gap: 8px; }
.ain input { width: 9em; max-width: 100%; font-variant-numeric: tabular-nums; }
.unit-s { color: var(--muted); }
.opts { display: grid; gap: 6px; }
.opts.row { grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); }
.opt { display: flex; align-items: center; gap: 8px; min-height: 44px; padding: 6px 10px; border: 1px solid var(--line); border-radius: var(--r); cursor: pointer; line-height: 1.3; }
.opt input { width: 20px; height: 20px; min-height: 0; margin: 0; accent-color: var(--accent); flex: none; }
.part.is-right input:not([type="radio"]) { border-color: var(--ok); background: var(--ok-soft); }
.part.is-wrong input:not([type="radio"]) { border-color: var(--bad); background: var(--bad-soft); }
.part.is-close input:not([type="radio"]), .part.is-unread input:not([type="radio"]) { border-color: var(--close); background: var(--close-soft); }
.fb { margin: 4px 0 0; font-size: 15px; line-height: 1.4; padding: 4px 8px; border-radius: var(--r); }
.fb.right { color: var(--ok); background: var(--ok-soft); }
.fb.wrong { color: var(--bad); background: var(--bad-soft); }
.fb.close, .fb.unread { color: var(--close); background: var(--close-soft); }
.qfoot { display: flex; gap: 10px; align-items: center; }
details.work { margin-top: 4px; border-top: 1px dashed var(--line); padding-top: 4px; }
details.work summary { cursor: pointer; color: var(--info); min-height: 44px; display: flex; align-items: center; font-weight: 600; }
.ans { margin: 8px 0 2px; }
.steps { margin: 0 0 4px; padding-left: 20px; color: var(--muted); font-size: 15.5px; }
.keyfig { margin: 6px 0 10px; max-width: 520px; }
.keyfig .meter { display: block; }
.keyfig .dialfig { max-width: 520px; }
.keyfig .meter.two { display: flex; }
.sheet-foot { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 14px; margin: 14px 0 6px; }
.ask { display: inline-flex; flex-wrap: wrap; align-items: center; gap: 6px 10px; background: var(--accent-soft); padding: 6px 10px; border-radius: var(--r); }
.share { margin: 16px 0 6px; }
.print-row { display: flex; flex-wrap: wrap; gap: 8px 12px; align-items: center; }
.print-row label { display: inline-flex; align-items: center; gap: 8px; font-weight: 600; }
.share-out label { display: grid; gap: 4px; font-weight: 600; margin-top: 8px; }
.share-out input { width: 100%; }
.recent { margin-top: 12px; background: var(--paper); border: 1px solid var(--line); border-radius: var(--r); padding: 4px 12px; }
.recent summary { cursor: pointer; min-height: 44px; display: flex; align-items: center; font-weight: 600; }
.recent ul { list-style: none; margin: 0; padding: 0; }
.recent li { display: flex; justify-content: space-between; align-items: center; gap: 10px; padding: 6px 0; border-top: 1px solid var(--line); }
.recent small { display: block; color: var(--muted); font-size: 14px; }
.hint { color: var(--muted); font-size: 14px; }
.toast { position: fixed; left: 50%; bottom: 16px; transform: translateX(-50%) translateY(150%); background: var(--ink); color: var(--paper); padding: 10px 16px; border-radius: var(--r); max-width: min(92vw, 520px); font-size: 15.5px; transition: transform 0.2s; z-index: 20; }
.toast.on { transform: translateX(-50%) translateY(0); }
@media (prefers-reduced-motion: reduce) { .toast { transition: none; } }

/* ---------- content ---------- */
.content { max-width: 72ch; padding: 26px 0 20px; }
.content h2 { font-size: 25px; margin: 26px 0 6px; }
.content ol { padding-left: 22px; }
table.ltab { border-collapse: collapse; width: 100%; font-size: 15px; font-variant-numeric: tabular-nums; background: var(--paper); }
table.ltab th, table.ltab td { border: 1px solid var(--line); padding: 5px 7px; text-align: left; }
table.ltab thead th { background: var(--bg); }
.faq details { border-top: 1px solid var(--line); }
.faq summary { cursor: pointer; font-weight: 600; padding: 10px 0; min-height: 44px; }
.faq p { margin: 0 0 12px; }
.sources { font-size: 14.5px; color: var(--muted); }
footer { border-top: 1px solid var(--line); padding: 16px 0 28px; font-size: 14.5px; color: var(--muted); }
.indep { margin: 0 0 10px; }
.sb-footer p { margin: 6px 0; }
.sb-more { line-height: 1.8; }
.print-root { display: none; }

@media (min-width: 900px) {
  .qbody { grid-template-columns: minmax(0, 1.8fr) minmax(0, 1fr); align-items: start; }
  .q.wide .qbody { grid-template-columns: 1fr; }
  .q.wide .qparts { grid-template-columns: 1fr 1fr; gap: 12px 22px; }
  .qparts .qfoot { grid-column: 1 / -1; }
  .keybody { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 4px 22px; align-items: start; }
  .keybody.nofig { grid-template-columns: 1fr; }
}
@media (max-width: 640px) {
  .setgrid { grid-template-columns: 1fr 1fr; }
  .setgrid .lvl { grid-column: 1 / -1; }
  #new { width: 100%; }
}
@media (max-width: 600px) {
  .zoom { display: inline-block; }
  .zoomed .figview { overflow-x: auto; overscroll-behavior-x: contain; }
  /* start at the left edge: a centered 640 px dial overflows both sides and its left part could not be scrolled to */
  .zoomed .figview .meter { flex-wrap: wrap; justify-content: flex-start; width: 640px; }
  .zoomed .figview .meter.two { width: 560px; }
  .zoomed .figview .meter.knobonly { width: auto; }
  .zoomed .figview .dialfig { flex: 0 0 auto; width: 640px; max-width: none; }
  .zoomed .figview .meter.two .dialfig { width: 560px; }
  /* the knob wraps under the wide dial; keep it in view while the dial scrolls sideways */
  .zoomed .figview .knobfig { position: sticky; left: 0; }
}
/* small phones: the dial runs the full width of the content, out to the card's edges */
@media (max-width: 380px) {
  .q .figview { margin-left: -13px; margin-right: -9px; }
  .q .dialfig figcaption { padding-left: 13px; }
  .q .keyfig { margin-left: -13px; margin-right: -9px; }
}
@media (max-width: 480px) {
  .sg span { font-size: 14px; padding: 4px 2px; }
  .hero { padding-top: 14px; }
  .lede { font-size: 16px; }
  .q { padding: 10px 10px 12px; }
  .meter { justify-content: center; }
  .dialfig { flex-basis: 100%; }
  .knobfig { flex: 0 0 190px; }
  .q { padding-left: 8px; padding-right: 8px; }
  table.ltab { font-size: 13.5px; }
  table.ltab th, table.ltab td { padding: 4px 4px; }
}

/* ---------- print ---------- */
@media print {
  :root { --ink: #000; --muted: #333; --line: #999; --paper: #fff; --edge: #555; --accent: #000; --face: #fff; --face-ink: #000; --mirror: #e4e4e4; --case: #000; }
  @page { margin: 10mm 12mm; }
  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; }
  .win { stroke: #000; stroke-width: 2; }
  .mirror { fill: #e4e4e4; stroke: #555; }
  .fig.use, .kl.use { fill: #000; font-weight: 800; text-decoration: underline; }
  .tru path { stroke: #000; }
  .rfl path { stroke: #555; }
  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: 4pt !important; }
  .ph { display: flex; justify-content: space-between; align-items: baseline; gap: 10pt; border-bottom: 2pt solid #000; margin-bottom: 4pt; }
  .ph h2 { font: 700 16pt var(--head); margin: 0; white-space: nowrap; }
  .ph p { margin: 0; font-size: 9pt; text-align: right; }
  .pmeta { display: flex; justify-content: space-between; gap: 12pt; margin: 4pt 0 2pt; }
  .plabel { margin: 0 0 3pt; font-size: 9pt; }
  .pq { list-style: none; margin: 0; padding: 0; }
  .pq > li { padding: 3pt 0 4pt; border-bottom: 0.75pt solid #999; break-inside: avoid; page-break-inside: avoid; }
  .pq h3, .pk h3 { font: 700 11.5pt var(--head); margin: 0 0 1pt; }
  .pscen { margin: 0 0 2pt; }
  .prow { display: grid; grid-template-columns: 108mm 1fr; gap: 0 5mm; align-items: start; }
  .prow.nofig { grid-template-columns: 1fr; }
  .pfig .meter { display: flex; flex-wrap: nowrap; gap: 3mm; align-items: flex-end; }
  .pfig .dialfig { flex: 0 0 auto; width: 75mm; max-width: none; }
  .pfig .knobfig { flex: 0 0 auto; width: 31mm; max-width: none; }
  .pfig .meter.two .dialfig { flex: 0 0 auto; width: 52mm; }
  /* zero error on the worksheet: the two dials stacked at full width, so one small division is well over 1 mm */
  .psheet .pfig .meter.two { flex-direction: column; align-items: flex-start; gap: 1.5mm; }
  .psheet .pfig .meter.two .dialfig { width: 86mm; }
  /* physics sheets: smaller single dials (30 or 50 divisions still read easily) so six questions fit a page */
  .psheet .pfig .dialfig:has(> svg.phy) { width: 66mm; }
  .psheet .pfig .meter.two .dialfig:has(> svg.phy) { width: 86mm; }
  .psheet .pq > li:has(svg.phy) { padding: 2pt 0 3pt; }
  .pk .prow:has(svg.phy) { grid-template-columns: 58mm 1fr; }
  .pk .pfig .dialfig:has(> svg.phy) { width: 56mm; }
  .pk .pfig .meter.two .dialfig:has(> svg.phy) { width: 27mm; }
  .pk > li:has(svg.phy) { padding: 2pt 0 3pt; }
  .pfig .meter.knobonly .knobfig { flex: 0 0 auto; width: 36mm; }
  .pfig figcaption { font-size: 8.5pt; color: #000; font-weight: 600; }
  .pparts { display: grid; gap: 1.5pt; font-size: 9.6pt; line-height: 1.28; }
  .pp p { margin: 0; }
  .pline { margin: 3pt 0 2pt !important; }
  .popts { display: grid; gap: 0; }
  .popts.two { grid-template-columns: 1fr 1fr; gap: 1pt 4mm; }
  .popts span { white-space: nowrap; }
  .pkey { break-before: page; page-break-before: always; }
  .pk { list-style: none; margin: 0; padding: 0; }
  .pk > li { padding: 4pt 0 5pt; border-bottom: 0.75pt solid #999; break-inside: avoid; page-break-inside: avoid; }
  .pk .prow { grid-template-columns: 78mm 1fr; }
  .pk .prow.nofig { grid-template-columns: 1fr; }
  .pk .pfig .dialfig { width: 74mm; }
  .pk .pfig .meter.two .dialfig { width: 37mm; }
  table.pkt { width: 100%; border-collapse: collapse; font-size: 9pt; table-layout: fixed; }
  table.pkt td { border-top: 0.5pt solid #bbb; padding: 2pt 3pt; vertical-align: top; }
  table.pkt td.pkq { width: 34%; }
  table.pkt td.pka { width: 22%; font-weight: 700; }
  .pkw { font-size: 8.5pt; }
}