/* Projection of Lines Practice: a drawing board in a first-year drawing hall. Pale sage ground, the problem sheet as
   off-white cartridge paper with a ruled border, graphite ink for the views, teal for construction (projectors, loci,
   arcs) and ochre for true lengths, as students colour their sheets with pencils. Headings in a condensed technical
   face with a title-block rule under them. Print: black only, weights and dashes carry the meaning, full size. */
[hidden] { display: none !important; }
:root {
  --bg: #eceee6;
  --paper: #fbfbf6;
  --sheet: #ffffff;
  --ink: #1d2422;
  --muted: #4c5653;
  --line: #d3d8cc;
  --edge: #7e8a83;
  --accent: #0d5c63;
  --accent-ink: #ffffff;
  --accent-soft: #dcebe9;
  --draw: #1a1f1e;
  --con: #0f6e75;
  --tl: #9a5a00;
  --ok: #1b6a35;
  --ok-soft: #e0f0e3;
  --close: #7a5200;
  --close-soft: #f5ead0;
  --bad: #a3231b;
  --bad-soft: #f8e1dd;
  --info: #23566b;
  --focus: #1d5fd1;
  --head: "Bahnschrift", "DIN Alternate", "Roboto Condensed", "Arial Narrow", "Helvetica Neue", Arial, 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: 2px;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #141a1b;
    --paper: #1c2324;
    --sheet: #1a2021;
    --ink: #e4e8e3;
    --muted: #adb7b2;
    --line: #313b3b;
    --edge: #6b7976;
    --accent: #6fc7cd;
    --accent-ink: #062a2d;
    --accent-soft: #173235;
    --draw: #eef1ee;
    --con: #6fc7cd;
    --tl: #f0b45a;
    --ok: #8fd8a3;
    --ok-soft: #15301d;
    --close: #f0c56b;
    --close-soft: #352a12;
    --bad: #ff9c8f;
    --bad-soft: #3a1c18;
    --info: #86c6e0;
    --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); }
.wrap { max-width: 1060px; 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 6px; max-width: 760px; }
h1 { font: 700 clamp(1.7rem, 4.6vw, 2.5rem)/1.1 var(--head); margin: 0 0 8px; letter-spacing: -0.005em; }
.lede { margin: 0; color: var(--muted); max-width: 64ch; }
h2 { font: 700 1.35rem/1.2 var(--head); margin: 0 0 10px; }

/* setup: one strip like a title block */
.setup { display: flex; flex-wrap: wrap; align-items: flex-end; gap: 10px 12px; padding: 12px 0; margin-top: 10px; border-top: 3px double var(--ink); }
.setup label, .print-row label { display: flex; flex-direction: column; gap: 3px; font-size: 0.85rem; font-weight: 650; color: var(--muted); }
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 18px; 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; }

.rules { border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.rules > summary { cursor: pointer; padding: 10px 0; min-height: 44px; font-weight: 650; display: flex; align-items: center; }
.rl { margin: 0 0 12px; padding-left: 1.3em; max-width: 78ch; }
.rl li { margin: 0 0 6px; }
.rl .src { color: var(--muted); font-size: 14px; display: block; }

.note { margin: 12px 0; padding: 10px 12px; border: 1px solid var(--close); background: var(--close-soft); overflow-wrap: anywhere; border-radius: var(--r); }
.note.info { border-color: var(--info); background: var(--paper); }
.note .link { min-height: 0; padding: 0; font-weight: 600; }

/* the problem sheet */
.sheet { background: var(--paper); border: 1px solid var(--edge); outline: 1px solid var(--edge); outline-offset: 4px; margin: 18px 5px 8px; padding: 14px 18px 10px; }
.sheet:focus { outline-color: var(--accent); }
.sheet-head { display: flex; justify-content: space-between; align-items: baseline; flex-wrap: wrap; gap: 4px 14px; border-bottom: 2px solid var(--ink); padding-bottom: 4px; }
.sheet-head h2 { margin: 0; }
.code { font-family: var(--mono); letter-spacing: 0.08em; color: var(--accent); }
.score { margin: 0; color: var(--muted); font-size: 0.95rem; }
.sline { margin: 6px 0 0; color: var(--muted); font-size: 0.92rem; }
.qs { list-style: none; margin: 0; padding: 0; }
.q { border-bottom: 1px solid var(--line); padding: 16px 0 10px; }
.q h3 { font: 700 1.12rem/1.3 var(--head); margin: 0 0 6px; display: flex; gap: 10px; align-items: baseline; }
.qn { font-family: var(--mono); color: var(--accent); font-weight: 700; min-width: 1.4em; }
.scen { margin: 0 0 10px; max-width: 72ch; }
.given svg, .keyfig svg { display: block; width: 100%; height: auto; background: var(--sheet); border: 1px solid var(--line); }
.given { margin: 4px 0 12px; }
.qparts { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 21rem), 1fr)); gap: 10px 22px; }
.part { margin: 0; border: 0; padding: 0; min-width: 0; }
.part.ch { grid-column: 1 / -1; }
.prompt, .part legend { display: block; font-size: 0.95rem; font-weight: 600; margin-bottom: 3px; padding: 0; }
.ain { display: inline-flex; align-items: center; gap: 6px; }
.ain input { width: 8.5em; font-family: var(--mono); }
.unit { color: var(--muted); min-width: 1.6em; }
.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); }
.opts { display: grid; gap: 6px; grid-template-columns: repeat(auto-fill, minmax(min(100%, 15rem), 1fr)); }
.opt { display: flex; gap: 8px; align-items: flex-start; min-height: 44px; padding: 9px 10px; border: 1px solid var(--line); border-radius: var(--r); background: var(--sheet); cursor: pointer; }
.opt input { margin: 3px 0 0; min-height: 0; width: 18px; height: 18px; accent-color: var(--accent); flex: none; }
.opt:has(input:checked) { border-color: var(--accent); box-shadow: inset 0 0 0 2px var(--accent); }
.fbwrap:empty { display: none; }
.fb { margin: 6px 0 0; padding: 6px 10px; border-radius: var(--r); max-width: 64ch; font-size: 0.95rem; }
.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); }
.qfoot { padding: 10px 0 0; }
.work > summary { cursor: pointer; color: var(--accent); font-weight: 600; padding: 10px 0; min-height: 44px; display: flex; align-items: center; }
.keyfig { margin: 4px 0 10px; }
/* phones: the key keeps a legible size and scrolls sideways inside its own box */
/* phones: the key fits the screen; Zoom in shows it full size, scrolling sideways inside its own box */
.khead { display: none; align-items: center; flex-wrap: wrap; gap: 4px 10px; margin: 0 0 6px; }
.khint { display: none; font-size: 0.9rem; color: var(--muted); }
.zoom { min-height: 40px; padding: 4px 12px; white-space: nowrap; }
@media (max-width: 560px) {
  .khead { display: flex; }
  #qs.zoomed .khint { display: inline; }
  #qs.zoomed .keyfig { overflow-x: auto; }
  #qs.zoomed .keyfig svg { min-width: 560px; }
}
.kt { border-collapse: collapse; width: 100%; font-size: 0.93rem; margin: 6px 0 10px; }
.kt th, .kt td { border-top: 1px solid var(--line); padding: 6px 8px 6px 0; text-align: left; vertical-align: top; }
.kt thead th { color: var(--muted); font-weight: 600; font-size: 0.85rem; border-top: 0; }
.kt tbody th { font-weight: 600; width: 34%; }
.kt .ka { font-family: var(--mono); white-space: nowrap; font-weight: 700; }
.kt .ka.kc { font-family: inherit; white-space: normal; }
.kt .ka small { font-weight: 400; color: var(--muted); }
.kt .kw { color: var(--muted); overflow-wrap: anywhere; }
@media (max-width: 640px) {
  .kt thead { display: none; }
  .kt tr { display: grid; grid-template-columns: 1fr auto; column-gap: 12px; border-top: 1px solid var(--line); padding: 6px 0; }
  .kt th, .kt td { border: 0; padding: 2px 0; }
  .kt tbody th { width: auto; }
  .kt .kw { grid-column: 1 / -1; font-size: 0.88rem; }
  .kt .ka { white-space: normal; max-width: 45vw; }
}
.work h4 { font: 700 1rem var(--head); margin: 6px 0 4px; }
.steps { margin: 0 0 10px; padding-left: 1.3em; font-size: 0.95rem; }
.steps li { margin-bottom: 4px; }
.sheet-foot { display: flex; align-items: center; flex-wrap: wrap; gap: 6px 16px; padding: 12px 0 4px; }
.hint { color: var(--muted); font-size: 0.9rem; }
.ask { display: flex; align-items: center; flex-wrap: wrap; gap: 8px; }

/* line work (stroke widths come from the drawing, in millimetres) */
svg.cons .ln { fill: none; stroke: var(--con); stroke-linecap: round; }
svg.cons .ln.view, svg.cons .ln.xy { stroke: var(--draw); }
svg.cons .ln.tl { stroke: var(--tl); }
svg.cons .ln.dim { stroke: var(--muted); }
svg.cons .ah { fill: var(--muted); }
svg.cons .dot { fill: var(--draw); }
svg.cons text { fill: var(--draw); font-family: Arial, "Helvetica Neue", var(--sans); }
svg.cons text.tg { fill: var(--tl); font-weight: 700; }
svg.cons text.al { fill: var(--con); }
svg.cons text.dt { fill: var(--muted); }
svg.cons.m-given .ln.proj { stroke: var(--muted); }

.share { padding: 8px 0 0; }
.print-row { display: flex; flex-wrap: wrap; align-items: flex-end; gap: 10px 12px; }
.share-out label { display: flex; flex-direction: column; gap: 3px; font-size: 0.9rem; font-weight: 600; margin-top: 8px; }
.share-out input { width: 100%; }
.recent { border-top: 1px solid var(--line); margin-top: 12px; }
.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(--ink); color: var(--bg); padding: 10px 14px; border-radius: var(--r); max-width: calc(100% - 32px); transition: transform 0.2s; pointer-events: none; z-index: 20; }
.toast.on { transform: translate(-50%, 0); }
@media (prefers-reduced-motion: reduce) { .toast { transition: none; } }

.content { padding: 28px 0 8px; max-width: 760px; }
.content h2 { margin-top: 26px; border-bottom: 1px solid var(--line); padding-bottom: 4px; }
.content p, .levels { max-width: 70ch; }
.levels { padding-left: 1.3em; }
.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); }
@media (max-width: 600px) {
  .sheet { margin: 14px 4px 8px; padding: 12px 10px 8px; }
  .setup .btn { flex: 1 1 auto; }
}

/* ---------- print ---------- */
.print-root { display: none; }
@page { margin: 8mm 12mm; }
@media print {
  :root { --ink: #000; --muted: #333; --line: #999; --paper: #fff; --sheet: #fff; --edge: #555; --draw: #000; --con: #000; --tl: #000; --accent: #000; }
  body { background: #fff; color: #000; font: 10pt/1.35 Arial, 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: 8pt Arial, sans-serif; color: #444; text-align: right; padding-bottom: 3pt !important; }
  section.psheet, section.pkey { break-before: page; page-break-before: always; }
  section:first-child { break-before: auto; page-break-before: auto; }
  .ph { border-bottom: 1.5pt solid #000; margin: 0 0 4pt; break-after: avoid; page-break-after: avoid; }
  .ph h2 { font: 700 14pt var(--head); margin: 0; }
  .ph p { margin: 0 0 3pt; font-size: 9pt; }
  .pmeta { display: flex; justify-content: space-between; gap: 12pt; margin: 4pt 0 8pt; }
  .pqs { list-style: none; margin: 0; padding: 0; }
  .pq { break-inside: avoid; page-break-inside: avoid; margin: 0 0 8pt; padding-top: 4pt; border-top: 0.75pt solid #000; }
  .pq h3 { font: 700 11pt var(--head); margin: 0 0 2pt; }
  .pscen { margin: 0 0 4pt; font-size: 10pt; }
  /* the frame is an outline, not a border: a border would take room inside the svg box (border-box) and shrink the
     full-size drawing by about 0.3% */
  .space svg { display: block; outline: 0.5pt solid #777; outline-offset: 0; max-width: 100%; }
  svg.cons .ln, svg.cons .ln.view, svg.cons .ln.tl { stroke: #000; }
  svg.cons .dot, svg.cons .ah { fill: #000; }
  svg.cons text, svg.cons text.tg, svg.cons text.al, svg.cons text.dt { fill: #000; }
  .pparts { list-style: none; margin: 4pt 0 0; padding: 0; display: grid; grid-template-columns: 1fr 1fr; gap: 3pt 14pt; }
  .pp { display: flex; align-items: flex-end; gap: 4pt; font-size: 9.5pt; min-height: 7mm; }
  .pp.wide { grid-column: 1 / -1; flex-wrap: wrap; }
  .pline { flex: 1 1 18mm; border-bottom: 0.5pt solid #555; min-width: 18mm; height: 1em; }
  .popts { display: inline-flex; flex-wrap: wrap; gap: 2pt 10pt; }
  /* a key keeps its drawing, steps and answer table on one page */
  .pkfig { break-inside: avoid; page-break-inside: avoid; }
  .pkbody { display: flex; flex-wrap: wrap; gap: 3mm 5mm; align-items: flex-start; }
  .pstepwrap { flex: 1 1 44mm; min-width: 44mm; }
  .pkbody.below .pstepwrap { flex-basis: 100%; }
  .pkbody.below .psteps { column-count: 2; column-gap: 6mm; }
  .psh { font: 700 9pt var(--head); margin: 0 0 1pt; }
  .psteps { margin: 0; padding-left: 12pt; font-size: 8pt; line-height: 1.3; }
  .psteps li { margin: 0 0 2pt; break-inside: avoid; }
  table.pkt { width: 100%; border-collapse: collapse; font-size: 8.5pt; margin-top: 4pt; break-inside: avoid; }
  table.pkt td { border: 0.5pt solid #555; padding: 1.5pt 3pt; vertical-align: top; }
  .pkq { width: 32%; font-weight: 700; }
  .pka { width: 15%; font-weight: 700; white-space: nowrap; }
  .pkw { font-size: 8pt; }
}