/* ===================================================================
   Textbook styles. theme.css supplies colours, buttons and cards;
   this file adds the two-column reader, figures, flowcharts, runnable
   examples, exam-check blocks and the listen (audiobook) bar.
   =================================================================== */

/* ---- layout ---- */
.bk { display: grid; grid-template-columns: 270px minmax(0, 1fr); gap: 28px;
  align-items: start; }
.bk-side { position: sticky; top: 74px; max-height: calc(100vh - 90px);
  overflow: auto; padding-right: 4px; }
.bk-side::-webkit-scrollbar { width: 6px; }
.bk-side::-webkit-scrollbar-thumb { background: #D5DDE7; border-radius: 6px; }
.bk-main { min-width: 0; }
@media (max-width: 900px) {
  .bk { grid-template-columns: 1fr; }
  .bk-side { position: static; max-height: none; }
  .bk-side.collapsed .toc { display: none; }
}

/* ---- table of contents ---- */
.toc-search { width: 100%; padding: 10px 13px; border: 1px solid var(--line);
  border-radius: 10px; font-size: 14px; font-family: inherit;
  background: rgba(255,255,255,.97); margin-bottom: 12px; }
.toc-search:focus { outline: 0; border-color: var(--saffron);
  box-shadow: 0 0 0 3px rgba(255,153,51,.16); }
.toc-unit { font-size: 11px; font-weight: 800; letter-spacing: .12em;
  text-transform: uppercase; color: var(--saffron-d); margin: 14px 0 6px; }
.toc a { display: flex; gap: 9px; align-items: flex-start; padding: 7px 9px;
  border-radius: 9px; text-decoration: none; color: var(--ink-2);
  font-size: 13.4px; line-height: 1.4; font-weight: 600; }
.toc a:hover { background: var(--saffron-pale); color: var(--saffron-d); }
.toc a.on { background: var(--saffron-pale); color: var(--saffron-d); }
.toc a .n { flex: 0 0 24px; height: 24px; border-radius: 7px; display: grid;
  place-items: center; font-size: 11.5px; font-weight: 800;
  background: #F1F4F8; color: var(--mut); }
.toc a.read .n { background: var(--green-pale); color: var(--green-d); }
.toc a.on .n { background: var(--saffron); color: #fff; }
.toc-tools { display: flex; gap: 7px; flex-wrap: wrap; margin-bottom: 10px; }
.toc .hidden { display: none; }
.toc-toggle { display: none; width: 100%; margin-bottom: 10px; }
@media (max-width: 900px) { .toc-toggle { display: inline-flex; } }

/* ---- listen bar ---- */
.listen { position: sticky; top: 60px; z-index: 20; display: flex; gap: 8px;
  align-items: center; flex-wrap: wrap; padding: 9px 12px; margin-bottom: 16px;
  background: rgba(255,255,255,.93); backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px); border: 1px solid var(--line);
  border-radius: 13px; box-shadow: var(--shadow); }
.listen .lbl { font-size: 12px; font-weight: 800; letter-spacing: .08em;
  text-transform: uppercase; color: var(--saffron-d); margin-right: 4px; }
.listen select { padding: 7px 9px; border: 1px solid var(--line);
  border-radius: 9px; font-family: inherit; font-size: 13px; max-width: 220px;
  background: #fff; }
.listen .st { font-size: 12.5px; color: var(--mut); font-weight: 600;
  margin-left: auto; }
.listen .prog { flex-basis: 100%; height: 4px; background: #EAEFF5;
  border-radius: 99px; overflow: hidden; margin-top: 2px; }
.listen .prog i { display: block; height: 100%; width: 0;
  background: linear-gradient(90deg, var(--saffron), var(--green)); }
.tts-on { background: #FFF7E8 !important; box-shadow: 0 0 0 3px #FFE3B8;
  border-radius: 6px; }
.tts-unsupported { display: none; }

/* ---- chapter body ---- */
.chapter { background: #fff; border: 1px solid var(--line);
  border-radius: var(--r); padding: 30px 36px 26px; box-shadow: var(--shadow);
  font-size: 16px; line-height: 1.75; color: var(--ink-2); }
@media (max-width: 640px) { .chapter { padding: 20px 16px; font-size: 15.5px; } }
.chapter.f-sm { font-size: 14.5px; } .chapter.f-lg { font-size: 17.5px; }
.chapter.f-xl { font-size: 19px; }
.ch-head { border-bottom: 1px solid var(--line); padding-bottom: 18px;
  margin-bottom: 22px; }
.ch-head h1 { font-size: 2em; line-height: 1.15; margin: 4px 0 12px;
  color: var(--ink); letter-spacing: -.6px; }
.ch-head .lead { font-size: 1.08em; color: var(--ink-2); margin: 0 0 14px; }
.ch-head .meta { font-size: .82em; color: var(--mut); font-weight: 600; }
.objectives { background: linear-gradient(90deg, var(--green-pale),
  rgba(233,247,231,.25)); border-left: 4px solid var(--green);
  padding: 12px 18px; border-radius: 0 12px 12px 0; margin: 14px 0 0; }
.objectives h2 { font-size: .8em; text-transform: uppercase;
  letter-spacing: .1em; color: var(--green-d); margin: 0 0 6px; }
.objectives ul { margin: 0; padding-left: 20px; }
.objectives li { margin: 3px 0; }

.chapter section { scroll-margin-top: 130px; margin-bottom: 30px; }
.chapter h2 { font-size: 1.45em; margin: 34px 0 12px; color: var(--ink);
  letter-spacing: -.3px; line-height: 1.25; display: flex; gap: 10px;
  align-items: center; flex-wrap: wrap; }
.chapter h2 .sec-listen { font-size: 12px; font-weight: 700; border: 1px solid
  var(--line); background: #fff; color: var(--mut); border-radius: 999px;
  padding: 3px 10px; cursor: pointer; font-family: inherit; }
.chapter h2 .sec-listen:hover { border-color: var(--saffron);
  color: var(--saffron-d); }
.chapter h3 { font-size: 1.15em; margin: 24px 0 8px; color: var(--ink); }
.chapter h4 { font-size: 1em; margin: 18px 0 6px; color: var(--ink); }
.chapter p { margin: 0 0 13px; }
.chapter p, .chapter li, .chapter dd, .chapter td, .chapter figcaption,
.chapter .callout { overflow-wrap: break-word; }
.chapter ul, .chapter ol { padding-left: 24px; margin: 0 0 13px; }
.chapter li { margin-bottom: 5px; }
.chapter li > ul, .chapter li > ol { margin: 5px 0 4px; }
.chapter b, .chapter strong { color: var(--ink); }
.chapter dl { margin: 0 0 13px; }
.chapter dt { font-weight: 800; color: var(--ink); margin-top: 8px; }
.chapter dd { margin: 2px 0 6px 20px; }
.chapter a { color: var(--saffron-d); font-weight: 600; }
.chapter code { font-size: .85em; }
.chapter pre.code { font-size: .84em; line-height: 1.6; white-space: pre;
  tab-size: 2; }
.chapter blockquote { margin: 14px 0; padding: 10px 18px; border-left: 4px solid
  #CBD5E1; background: #F8FAFC; border-radius: 0 10px 10px 0; font-style:
  italic; }
.chapter table.tbl { font-size: .9em; }
.chapter table.tbl code { white-space: nowrap; }
.chapter .tbl-wrap { overflow-x: auto; margin: 0 0 15px; }
.chapter .tbl-wrap table.tbl { margin: 0; min-width: 480px; }
.chapter kbd { background: #F1F5F9; border: 1px solid #CBD5E1;
  border-bottom-width: 2px; border-radius: 5px; padding: 1px 6px;
  font-family: var(--mono); font-size: .82em; }

/* callouts */
.chapter .callout { margin: 16px 0; font-size: .95em; }
.chapter .callout b:first-child { color: var(--saffron-d); }
.chapter .callout.exam { background: linear-gradient(90deg, #EEF2FF,
  rgba(238,242,255,.3)); border-left-color: #4F46E5; }
.chapter .callout.exam b:first-child { color: #3730A3; }
.chapter .callout.warn { background: linear-gradient(90deg, var(--bad-bg),
  rgba(253,240,240,.3)); border-left-color: var(--bad); }
.chapter .callout.warn b:first-child { color: var(--bad); }
.chapter .callout.why { background: linear-gradient(90deg, var(--green-pale),
  rgba(233,247,231,.3)); border-left-color: var(--green); }
.chapter .callout.why b:first-child { color: var(--green-d); }
.chapter .callout p { margin: 6px 0 0; }

/* wrong / right pairs */
.fix { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin: 12px 0
  16px; }
@media (max-width: 700px) { .fix { grid-template-columns: 1fr; } }
.fix > div { border-radius: 11px; padding: 11px 14px; font-size: .9em; }
.fix .w { background: var(--bad-bg); border: 1px solid #F1B4B4; }
.fix .r { background: var(--ok-bg); border: 1px solid #A9E3C4; }
.fix .w > b { color: var(--bad); } .fix .r > b { color: var(--ok); }
.fix pre { margin: 6px 0 0; background: rgba(255,255,255,.7); color: var(--ink);
  border-radius: 8px; padding: 8px 10px; font-family: var(--mono);
  font-size: .9em; line-height: 1.5; white-space: pre-wrap; }

/* figures and flowcharts */
.fig { margin: 18px 0 22px; padding: 14px 14px 10px; border: 1px solid
  var(--line); border-radius: 14px; background: #FCFDFE; }
.fig svg { width: 100%; height: auto; display: block; }
.fig svg text { font-family: var(--font); }
.fig svg .mono { font-family: var(--mono); }
.fig figcaption { font-size: .86em; color: var(--mut); margin-top: 8px;
  line-height: 1.5; text-align: center; }
.fig figcaption b { color: var(--ink); }
.fig.narrow svg { max-width: 560px; margin: 0 auto; }
.fig.tiny svg { max-width: 380px; margin: 0 auto; }
/* shared SVG classes */
svg .box { fill: #fff; stroke: #0B2545; stroke-width: 1.6; }
svg .box.saf { fill: var(--saffron-pale); stroke: var(--saffron-d); }
svg .box.grn { fill: var(--green-pale); stroke: var(--green); }
svg .box.blu { fill: #EEF2FF; stroke: #4F46E5; }
svg .box.gry { fill: #F1F4F8; stroke: #94A3B8; }
svg .box.red { fill: var(--bad-bg); stroke: var(--bad); }
svg .box.ink { fill: #0E1B2E; stroke: #0E1B2E; }
svg .t { fill: var(--ink); font-size: 13px; }
svg .t.b { font-weight: 800; }
svg .t.s { font-size: 11px; fill: var(--mut); }
svg .t.w { fill: #fff; }
svg .t.c { text-anchor: middle; }
svg .edge { fill: none; stroke: #3C4A60; stroke-width: 1.7; }
svg .edge.saf { stroke: var(--saffron-d); }
svg .edge.grn { stroke: var(--green); }
svg .edge.dash { stroke-dasharray: 5 4; }
svg .dec { fill: #FFF1E0; stroke: var(--saffron-d); stroke-width: 1.6; }
svg .cap { fill: #0B2545; font-size: 11px; font-weight: 800;
  letter-spacing: .06em; }

/* runnable examples */
.ex { margin: 14px 0 20px; border: 1px solid var(--line); border-radius: 13px;
  overflow: hidden; background: #fff; }
.ex .ex-bar { display: flex; gap: 8px; align-items: center; padding: 7px 10px
  7px 14px; background: #F7F9FC; border-bottom: 1px solid var(--line);
  font-size: 12.5px; font-weight: 700; color: var(--mut); flex-wrap: wrap; }
.ex .ex-bar .sp { flex: 1; }
.ex .ex-bar button { font-size: 12.5px; padding: 6px 11px; border-radius: 8px; }
.ex pre.code { margin: 0; border-radius: 0; max-height: 420px; }
.ex iframe { display: none; width: 100%; border: 0; border-top: 3px solid
  var(--saffron); background: #fff; height: 240px; }
.ex iframe.on { display: block; }
.ex.tall iframe { height: 380px; }
.ex .out { display: none; padding: 12px 16px; border-top: 3px solid
  var(--saffron); }
.ex .out.on { display: block; }

/* console panel under a JavaScript example (filled by runshim.js) */
.ex .rc { border-top: 1px solid #22324A; background: #0F1B2D; color: #E6EDF7;
  font-family: var(--mono); font-size: 12.8px; line-height: 1.5; }
.ex .rc[hidden] { display: none; }
.ex .rc-head { display: flex; align-items: center; justify-content: space-between;
  padding: 5px 10px 5px 14px; background: #16243A; color: #93A9C7;
  font: 800 11px/1 var(--font); letter-spacing: .1em; text-transform: uppercase; }
.ex .rc-clear { background: none; border: 1px solid #33465F; color: #B9C7DA;
  border-radius: 6px; padding: 3px 9px; font: 600 11px var(--font); cursor: pointer; }
.ex .rc-body { max-height: 240px; overflow: auto; }
.rc-line { padding: 4px 14px; border-bottom: 1px solid rgba(255,255,255,.06);
  white-space: pre-wrap; overflow-wrap: anywhere; }
.rc-line.rc-warn { color: #FFD58A; background: rgba(255,200,0,.07); }
.rc-line.rc-error { color: #FFA3A3; background: rgba(255,80,80,.09); }
.rc-line.rc-info { color: #9FD3FF; }
.rc-line.rc-empty { color: #7D8DA3; font-style: italic; }
.rc-table { border-collapse: collapse; margin: 2px 0; }
.rc-table th, .rc-table td { border: 1px solid #33465F; padding: 2px 8px; text-align: left; }
.rc-table th { color: #93A9C7; }


/* live demo boxes (rendered directly on the page) */
.demo { margin: 12px 0 18px; padding: 14px 16px; border: 1px dashed #CBD5E1;
  border-radius: 12px; background: #FBFCFE; font-size: .95em; }
.demo .dlab { font-size: 11px; font-weight: 800; letter-spacing: .1em;
  text-transform: uppercase; color: var(--mut); margin: 0 0 8px; }
.demo input, .demo select, .demo textarea, .demo button { font-family: inherit;
  font-size: 14px; }
.demo input:not([type=checkbox]):not([type=radio]):not([type=range]):not([type=color]),
.demo select, .demo textarea { padding: 6px 9px; border: 1px solid #CBD5E1;
  border-radius: 7px; }
.demo label { display: inline-block; margin: 3px 12px 3px 0; }
.demo table { border-collapse: collapse; }
.demo table th, .demo table td { border: 1px solid #94A3B8; padding: 6px 10px; }
.demo table th { background: #F1F4F8; }
.demo table caption { font-weight: 700; padding: 4px; }
.demo .row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center;
  margin: 6px 0; }

/* exam-style checks */
.exam .q { border: 1px solid var(--line); border-radius: 11px; margin: 0 0 9px;
  background: #fff; }
.exam .q summary { cursor: pointer; padding: 11px 15px; font-weight: 700;
  color: var(--ink); list-style: none; display: flex; gap: 10px;
  overflow-wrap: anywhere; min-width: 0; }
.exam .q summary::-webkit-details-marker { display: none; }
.exam .q summary::before { content: "Q"; flex: 0 0 24px; height: 24px;
  border-radius: 7px; background: #EEF2FF; color: #3730A3; display: grid;
  place-items: center; font-size: 12px; }
.exam .q[open] summary { border-bottom: 1px solid var(--line); }
.exam .q .a { padding: 11px 15px 6px; font-size: .95em; }
.exam .q .a > b:first-child { color: var(--ok); }
.exam .opts { margin: 4px 0 8px 0; padding-left: 20px; }
.exam .opts li { margin: 2px 0; }
.exam .lvl { font-size: 11px; font-weight: 800; padding: 2px 8px;
  border-radius: 999px; background: #F1F4F8; color: var(--mut);
  margin-left: auto; align-self: center; white-space: nowrap; }

/* key takeaways + revision table */
.kt { background: linear-gradient(120deg, #FFF3E4, #FFFFFF 60%, #E9F7E7);
  border: 1px solid var(--line); border-radius: 14px; padding: 16px 20px;
  margin: 10px 0 18px; }
.kt h3 { margin: 0 0 8px; }
.kt ol, .kt ul { margin: 0; }

/* chapter footer nav */
.ch-nav { display: flex; gap: 10px; justify-content: space-between;
  flex-wrap: wrap; margin-top: 26px; padding-top: 18px; border-top: 1px solid
  var(--line); }
.ch-nav a, .ch-nav button { max-width: 48%; }
@media (max-width: 640px) { .ch-nav a, .ch-nav button { max-width: none;
  width: 100%; } }

/* book home (cover) */
.cover { display: grid; grid-template-columns: 1.1fr .9fr; gap: 26px;
  align-items: center; margin-bottom: 26px; }
@media (max-width: 800px) { .cover { grid-template-columns: 1fr; } }
.cover h1 { font-size: 34px; line-height: 1.15; margin: 8px 0 12px;
  letter-spacing: -.8px; }
.cover p { line-height: 1.7; color: var(--ink-2); }
.cover .art svg { width: 100%; height: auto; }
.units { display: grid; gap: 14px; grid-template-columns: repeat(auto-fit,
  minmax(300px, 1fr)); margin-bottom: 26px; }
.unit-card { background: #fff; border: 1px solid var(--line);
  border-radius: var(--r); padding: 18px 20px; box-shadow: var(--shadow); }
.unit-card h2 { font-size: 17px; margin: 0 0 4px; }
.unit-card p { color: var(--mut); font-size: 13.5px; margin: 0 0 10px; }
.unit-card ol { margin: 0; padding-left: 22px; font-size: 14px;
  line-height: 1.75; }
.unit-card ol a { text-decoration: none; color: var(--ink-2); font-weight: 600; }
.unit-card ol a:hover { color: var(--saffron-d); }
.unit-card ol li.read a::after { content: " \2713"; color: var(--green-d); }

/* search results */
.sr { border: 1px solid var(--line); border-radius: 11px; padding: 11px 14px;
  margin-bottom: 8px; background: #fff; cursor: pointer; }
.sr:hover { border-color: var(--saffron); }
.sr .h { font-weight: 800; color: var(--ink); font-size: 14px; }
.sr .c { font-size: 12px; color: var(--saffron-d); font-weight: 700; }
.sr .s { font-size: 13px; color: var(--mut); margin-top: 3px; line-height: 1.5; }
.sr mark { background: #FFE9A8; padding: 0 2px; border-radius: 3px; }

/* reading progress line */
.rprog { position: fixed; top: 60px; left: 0; height: 3px; width: 0;
  background: linear-gradient(90deg, var(--saffron), var(--green)); z-index: 40;
  transition: width .15s; }

@media print {
  .bk { display: block; }
  .bk-side, .listen, .ch-nav, .rprog, .ex .ex-bar, .sec-listen,
  .toc-toggle { display: none !important; }
  .chapter { border: 0; box-shadow: none; padding: 0; font-size: 12pt; }
  .exam .q { break-inside: avoid; }
  .exam .q .a { display: block; }
  .exam .q summary::before { content: "Q "; }
  .ex pre.code { max-height: none; white-space: pre-wrap; }
  .fig { break-inside: avoid; }
}

/* ===================================================================
   PLAIN-LANGUAGE LAYER
   Teaching devices added for Unit 3 (and usable in any chapter):
   a prerequisite box, plain-words restatements, analogies, tap-to-
   explain jargon words, inline quick checks and live CSS sliders.
   =================================================================== */

/* ---- "Before you start": what you need to know, and where it was ---- */
.prereq { background: linear-gradient(90deg, #EEF2FF, rgba(238,242,255,.25));
  border-left: 4px solid #4F46E5; border-radius: 0 12px 12px 0;
  padding: 12px 18px; margin: 14px 0 0; }
.prereq h2 { font-size: .8em; text-transform: uppercase; letter-spacing: .1em;
  color: #3730A3; margin: 0 0 6px; }
.prereq ul { margin: 0; padding-left: 20px; }
.prereq li { margin: 3px 0; }

/* ---- "In plain words": the same idea at the kitchen table ---- */
.plain { background: #FFFDF6; border: 1px dashed #E8C583; border-radius: 12px;
  padding: 11px 16px 12px; margin: 15px 0; }
.plain::before { content: "In plain words"; display: block; font-size: 11px;
  font-weight: 800; letter-spacing: .1em; text-transform: uppercase;
  color: #B45309; margin-bottom: 5px; }
.plain p { margin: 0 0 8px; }
.plain p:last-child, .plain ul:last-child, .plain ol:last-child { margin-bottom: 0; }

/* ---- analogy: the everyday picture ---- */
.chapter .callout.analogy { background: linear-gradient(90deg, #F5F3FF,
  rgba(245,243,255,.3)); border-left-color: #7C3AED; }
.chapter .callout.analogy b:first-child { color: #6D28D9; }

/* ---- jargon word: tap it for a one-line meaning ---- */
.jw { border-bottom: 2px dotted var(--saffron-d); color: var(--saffron-d);
  font-weight: 600; cursor: pointer; padding: 0 1px; border-radius: 3px; }
.jw:hover, .jw.on { background: var(--saffron-pale); }
.jw:focus-visible { outline: 2px solid var(--saffron-d); outline-offset: 2px; }
.jw-pop { display: block; margin: 9px 0; background: #FFF8EB;
  border-left: 3px solid var(--saffron); border-radius: 0 9px 9px 0;
  padding: 9px 14px; font-size: .92em; line-height: 1.65; color: var(--ink-2);
  font-weight: 400; }
.jw-pop b { color: var(--saffron-d); }
.wordnote { font-size: .86em; color: var(--mut); margin: 10px 0 0;
  border-top: 1px dashed var(--line); padding-top: 9px; }

/* ---- inline quick check: friendlier than the end-of-chapter exam ---- */
details.qc { border: 1px solid #CFE6D8; background: #F4FBF6; border-radius: 11px;
  margin: 14px 0; }
details.qc summary { cursor: pointer; padding: 10px 15px; font-weight: 700;
  color: #0A5C34; list-style: none; display: flex; gap: 9px;
  overflow-wrap: anywhere; }
details.qc summary::-webkit-details-marker { display: none; }
details.qc summary::before { content: "\2753"; flex: 0 0 auto; }
details.qc[open] summary { border-bottom: 1px solid #CFE6D8; }
details.qc .a { padding: 11px 15px; font-size: .95em; }
details.qc .a p:last-child { margin-bottom: 0; }

/* ---- live CSS sliders: change a value, watch the box AND the code ---- */
.tryit { border: 1px solid var(--line); border-radius: 14px; overflow: hidden;
  margin: 16px 0 20px; background: #fff; box-shadow: var(--shadow); }
.tryit-head { background: #F7F9FC; border-bottom: 1px solid var(--line);
  padding: 8px 14px; font-size: 12.5px; font-weight: 700; color: var(--mut);
  display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.tryit-head .sp { flex: 1; }
.tryit-reset { font-size: 12px; font-weight: 700; border: 1px solid var(--line);
  background: #fff; color: var(--mut); border-radius: 999px; padding: 3px 11px;
  cursor: pointer; font-family: inherit; }
.tryit-reset:hover { border-color: var(--saffron); color: var(--saffron-d); }
.tryit-stage { padding: 22px 18px; display: grid; place-items: center;
  min-height: 110px; overflow: auto;
  background: repeating-conic-gradient(#F2F6FA 0% 25%, #fff 0% 50%) 50% / 18px 18px; }
.tryit-stage .frame { background: #fff; border: 2px dashed #B9C6D6;
  border-radius: 8px; padding: 10px; width: 100%; max-width: 420px; }
.tryit-ctl { display: grid; gap: 10px 18px; padding: 13px 16px;
  grid-template-columns: repeat(auto-fit, minmax(215px, 1fr));
  border-top: 1px solid var(--line); background: #FBFCFE; }
.tryit-ctl label { display: grid; grid-template-columns: 1fr auto;
  align-items: center; gap: 3px 8px; font-family: var(--mono); font-size: 12px;
  font-weight: 700; color: var(--ink-2); }
.tryit-ctl input[type="range"] { grid-column: 1 / -1; width: 100%;
  accent-color: var(--saffron-d); }
.tryit-ctl select, .tryit-ctl input[type="color"], .tryit-ctl input[type="text"] {
  grid-column: 1 / -1; font-family: var(--mono); font-size: 12.5px;
  padding: 5px 7px; border: 1px solid var(--line); border-radius: 7px;
  background: #fff; width: 100%; }
.tryit-ctl input[type="color"] { padding: 2px; height: 30px; }
.tryit-ctl .tv { font-family: var(--mono); font-size: 11.5px; font-weight: 800;
  color: var(--saffron-d); }
.tryit-css { margin: 0; border-top: 1px solid var(--line); background: var(--code);
  color: #DCE7F5; font-family: var(--mono); font-size: 12.5px; line-height: 1.65;
  padding: 12px 16px; white-space: pre; overflow-x: auto; }
.tryit-css .hl { color: #FFD08A; font-weight: 700; }
.tryit-css .sel { color: #7FD1A8; }
@media (max-width: 520px) { .tryit-ctl { grid-template-columns: 1fr; } }

/* a plain swatch row, for colour and unit chapters */
.swatches { display: grid; gap: 9px; margin: 14px 0 18px;
  grid-template-columns: repeat(auto-fit, minmax(122px, 1fr)); }
.swatches .sw { border: 1px solid var(--line); border-radius: 11px;
  overflow: hidden; background: #fff; }
.swatches .sw i { display: block; height: 46px; }
.swatches .sw span { display: block; padding: 6px 9px; font-family: var(--mono);
  font-size: 11.5px; color: var(--ink-2); line-height: 1.45; }

@media print {
  .tryit-ctl, .tryit-head { display: none !important; }
  .jw { border-bottom: 0; color: inherit; }
  details.qc .a { display: block; }
}

/* ============================================================
   REFERENCE MATERIAL
   Per-chapter "Reference material" sections and the Reference
   Shelf appendix (Chapter 40). Links are external and always
   carry a visible reason to open them.
   ============================================================ */
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;
  overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0}

.chapter .lead-sm{font-size:.95rem;color:var(--mut);margin:0 0 14px;
  max-width:62ch}

.refs ul{list-style:none;padding:0;margin:0;display:grid;gap:10px}
.refs ul li{margin:0;padding:12px 14px;border:1px solid var(--line);
  border-radius:10px;background:var(--card);
  border-left:3px solid var(--saffron)}
.refs ul li > a{font-weight:700;text-decoration:none;
  border-bottom:1px solid transparent;display:inline-block}
.refs ul li > a:hover,.refs ul li > a:focus-visible{
  border-bottom-color:currentColor}
.refs ul li > b{font-weight:700;color:var(--ink);display:inline-block}
.refs .ext{font-size:.85em;margin-left:4px;opacity:.7}
.refs .why{display:block;margin-top:4px;font-size:.9rem;color:var(--mut);
  line-height:1.55}
.refs-foot{margin:14px 0 0;font-size:.88rem;color:var(--mut)}

/* the shelf appendix groups links under numbered headings */
#ch40 .refs{margin-bottom:26px}
#ch40 .refs ul li{border-left-color:var(--green)}

@media print{
  .refs ul li{break-inside:avoid;border-left-width:2px}
  .refs .ext{display:none}
  .refs ul li > a::after{content:" (" attr(href) ")";font-weight:400;
    font-size:.82em;word-break:break-all}
}

/* ============================================================
   READABLE DIAGRAMS ON SMALL SCREENS
   A figure is drawn in a 600-720 unit viewBox. Inside a phone's
   ~270px text column that shrinks 11px labels to about 4px, so
   on narrow screens the figure breaks out of the column and
   scrolls sideways at a legible minimum width. Every figure
   also gets a full-screen view.
   ============================================================ */
.chapter .fig { position: relative; }
.chapter .fig-scroll { overflow-x: auto; overflow-y: hidden;
  -webkit-overflow-scrolling: touch; }

.chapter .fig-zoom { position: absolute; top: 8px; right: 8px; z-index: 2;
  font: 600 11.5px/1 var(--font); color: var(--mut); cursor: pointer;
  background: rgba(255,255,255,.92); border: 1px solid var(--line);
  border-radius: 999px; padding: 5px 10px; display: inline-flex; gap: 5px;
  align-items: center; opacity: 0; transition: opacity .15s ease; }
.chapter .fig:hover .fig-zoom, .chapter .fig-zoom:focus-visible { opacity: 1; }
.chapter .fig-zoom:hover { color: var(--ink); border-color: var(--saffron); }

/* the swipe hint only appears when the diagram really is cut off */
.chapter .fig.is-scrollable::after { content: "swipe to see all \2192";
  position: absolute; left: 16px; top: 8px; font-size: 10.5px;
  font-weight: 700; letter-spacing: .02em; color: var(--saffron-d);
  background: var(--saffron-pale); border-radius: 999px; padding: 4px 9px;
  pointer-events: none; }

@media (max-width: 760px) {
  /* full-bleed: use the whole phone width, not just the text column */
  .chapter .fig { margin-left: -16px; margin-right: -16px;
    padding-left: 0; padding-right: 0; border-radius: 0;
    border-left: 0; border-right: 0; }
  .chapter .fig-scroll { padding: 0 16px; }
  .chapter .fig figcaption { padding: 0 16px; }
  .chapter .fig svg { min-width: 660px; }          /* keeps labels ~10px */
  .chapter .fig.narrow svg, .chapter .fig.tiny svg { max-width: none; }
  .chapter .fig-zoom { opacity: 1; }               /* no hover on touch */
}

/* ---- full-screen diagram view ---- */
.fig-lightbox { position: fixed; inset: 0; z-index: 9000; display: flex;
  flex-direction: column; background: rgba(10,18,32,.93); }
.fig-lb-bar { display: flex; gap: 8px; align-items: center; padding: 10px 12px;
  border-bottom: 1px solid rgba(255,255,255,.14); flex: 0 0 auto; }
.fig-lb-hint { color: #B9C6D8; font: 600 12px/1.3 var(--font); margin-right: auto; }
.fig-lb-btn { font: 700 15px/1 var(--font); color: #fff; cursor: pointer;
  background: rgba(255,255,255,.12); border: 1px solid rgba(255,255,255,.22);
  border-radius: 9px; min-width: 40px; padding: 9px 12px; }
.fig-lb-btn:hover { background: rgba(255,255,255,.22); }
.fig-lb-btn.close { background: var(--saffron); border-color: var(--saffron);
  color: #22160A; font-size: 20px; }
.fig-lb-stage { flex: 1 1 auto; overflow: auto; padding: 16px;
  display: flex; flex-direction: column; align-items: flex-start; }
.fig-lb-stage svg { height: auto; background: #fff; border-radius: 10px;
  padding: 12px; min-width: 0; }
.fig-lb-cap { color: #D7E0EC; font-size: 13px; line-height: 1.5; margin: 12px 0 0;
  max-width: 70ch; }
.fig-lb-cap b { color: #fff; }
@media (max-width: 560px) { .fig-lb-hint { display: none; } }

@media print {
  .fig-zoom, .fig.is-scrollable::after { display: none !important; }
  .chapter .fig-scroll { overflow: visible; }
  .chapter .fig svg { min-width: 0; }
}