/* Visual Learn house style. See house-style/README.md.
   Copy these rules into an explainer (inline <style> or its own styles.css);
   explainers never link to this file. Page-specific rules go after it. */

:root {
  color-scheme: light;

  /* paper and ink */
  --paper: #fcfbf7;
  --wash: #f3f1ea;          /* the only fill for a region that must read as "a thing" */
  --ink: #1c1b18;
  --ink-2: #57544c;         /* secondary text, captions */
  --ink-3: #716d63;         /* tertiary: ticks, meta, disabled */
  --rule: #e2ded3;          /* hairlines, gridlines */
  --rule-2: #c9c4b6;        /* control borders, axis lines */
  --link: #1f4e79;

  /* data colors: muted, colorblind-checked (derived from Okabe-Ito).
     Each page maps entities to these once and never reassigns them. */
  --c-blue:   #2f6ea6;
  --c-orange: #ae5019;
  --c-green:  #23765b;
  --c-purple: #6a51a3;
  --c-red:    #b8433a;
  --c-gold:   #b8901f;
  --c-sky:    #6ea8d6;
  --c-grey:   #a8a396;      /* context data: everything not being discussed */

  --serif: "Source Serif 4", "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --sans: "Source Sans 3", -apple-system, "Segoe UI", system-ui, sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, "SF Mono", Menlo, Consolas, monospace;

  /* the grid: a reading column, a gutter, and a margin for notes */
  --text: 37rem;
  --gap: 2.5rem;
  --margin: 15rem;
  --page: calc(var(--text) + var(--gap) + var(--margin));
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 3.5rem; }
body {
  margin: 0; background: var(--paper); color: var(--ink);
  font-family: var(--serif); font-size: 1.1875rem; line-height: 1.58;
  font-optical-sizing: auto; -webkit-font-smoothing: antialiased;
  counter-reset: sidenote figure;
}
::selection { background: #e8dfc3; }
:focus-visible { outline: 3px solid var(--link); outline-offset: 3px; }

/* ---------- page frame ---------- */
.page { max-width: calc(var(--page) + 3rem); margin: 0 auto; padding: 0 1.5rem 6rem; }
.page > :not(section), section > * { max-width: var(--text); }
.page > .wide, section > .wide { max-width: none; }
.page > h1 { max-width: 48rem; }

/* ---------- type ---------- */
h1, h2, h3 { font-weight: 400; color: var(--ink); text-wrap: balance; }
h1 { font-size: clamp(2.5rem, 5.5vw, 3.6rem); line-height: 1.04; letter-spacing: -0.012em; margin: 4.5rem 0 0.6rem; }
.subtitle { font-style: italic; font-size: 1.45rem; line-height: 1.35; color: var(--ink-2); margin: 0 0 2rem; }
h2 { font-size: 1.95rem; line-height: 1.15; letter-spacing: -0.005em; margin: 4.5rem 0 1rem; }
h3 { font-style: italic; font-size: 1.35rem; line-height: 1.25; margin: 2.5rem 0 0.6rem; }
p, ul, ol { margin: 0 0 1.1rem; text-wrap: pretty; }
ul, ol { padding-left: 1.3rem; }
li { margin-bottom: 0.35rem; }
li::marker { color: var(--ink-3); }
strong, b { font-weight: 600; }
em, i { font-style: italic; }
.lede { font-size: 1.3rem; line-height: 1.5; }
.meta { font-family: var(--sans); font-size: 0.8125rem; color: var(--ink-3); letter-spacing: 0.01em; }
.smallcaps { font-variant-caps: all-small-caps; letter-spacing: 0.04em; }
a { color: var(--link); text-decoration-line: underline; text-decoration-thickness: 1px; text-underline-offset: 0.16em; text-decoration-color: color-mix(in srgb, var(--link) 35%, transparent); }
a:hover { text-decoration-color: currentColor; }
hr { border: 0; border-top: 1px solid var(--rule); margin: 3rem 0; }

code, kbd, samp { font-family: var(--mono); font-size: 0.84em; }
pre { font-family: var(--mono); font-size: 0.82rem; line-height: 1.55; margin: 0 0 1.25rem; padding: 0.1rem 0 0.1rem 1rem; border-left: 1px solid var(--rule-2); overflow-x: auto; }
.num, table, svg text, .controls { font-variant-numeric: lining-nums tabular-nums; }

/* ---------- sidenotes and margin notes ----------
   <span class="sn-ref"></span><span class="sidenote">…</span>  numbered, inside the paragraph
   <span class="marginnote">…</span>                              unnumbered
   Wide screens: floated into the margin column. Narrow: an indented block. */
.sidenote, .marginnote {
  float: right; clear: right; width: var(--margin);
  margin: 0.3rem calc(-1 * (var(--margin) + var(--gap))) 1rem 0;
  font-size: 0.875rem; line-height: 1.45; color: var(--ink-2);
  font-style: normal; font-weight: 400;
}
.sn-ref { counter-increment: sidenote; }
.sn-ref::after { content: counter(sidenote); font-family: var(--sans); font-size: 0.66em; font-weight: 600; vertical-align: super; line-height: 0; margin-left: 0.08em; color: var(--ink-2); }
.sidenote::before { content: counter(sidenote) "\2002"; font-family: var(--sans); font-size: 0.8em; font-weight: 600; }
p, li, figure { position: relative; }

/* ---------- figures ----------
   <figure class="fig">          text-column width, caption in the margin on wide screens
   <figure class="fig wide">     full page width, caption below
   Inside: optional .controls, the graphic, then <figcaption>. No borders, no cards. */
figure { margin: 2.25rem 0 2.5rem; padding: 0; }
.fig { counter-increment: figure; }
.fig figcaption { font-size: 0.9375rem; line-height: 1.5; color: var(--ink-2); margin-top: 0.85rem; max-width: var(--text); }
.fig figcaption .fig-n::before { content: "Figure " counter(figure) ". "; font-family: var(--sans); font-weight: 600; font-size: 0.78rem; letter-spacing: 0.02em; color: var(--ink); }
.fig .takeaway { font-style: italic; color: var(--ink); }
.graphic { position: relative; }
.graphic svg { display: block; width: 100%; height: auto; overflow: visible; }
.scroll-x { overflow-x: auto; overscroll-behavior-x: contain; }
.scroll-x > * { min-width: var(--min, 36rem); }

/* ---------- controls: quiet, real, keyboard reachable ---------- */
.controls { display: flex; flex-wrap: wrap; align-items: center; gap: 0.6rem 1.4rem; margin: 0 0 0.9rem; font-family: var(--sans); font-size: 0.875rem; color: var(--ink-2); }
.control { display: inline-flex; align-items: center; gap: 0.55rem; }
.control > .label { color: var(--ink-2); }
.control > output, .readout { font-family: var(--sans); color: var(--ink); font-weight: 600; min-width: 3.2ch; }
.btn {
  font: 500 0.875rem/1 var(--sans); color: var(--ink); background: transparent;
  border: 1px solid var(--rule-2); border-radius: 3px; padding: 0.5rem 0.75rem; min-height: 2.125rem;
  cursor: pointer; display: inline-flex; align-items: center; gap: 0.4rem;
}
.btn:hover { border-color: var(--ink-2); }
.btn:disabled { color: var(--ink-3); border-color: var(--rule); cursor: default; }
.btn.primary { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.seg { display: inline-flex; border: 1px solid var(--rule-2); border-radius: 3px; overflow: hidden; }
.seg > button { font: 500 0.875rem/1 var(--sans); color: var(--ink-2); background: transparent; border: 0; padding: 0.5rem 0.75rem; min-height: 2.125rem; cursor: pointer; }
.seg > button + button { border-left: 1px solid var(--rule); }
.seg > button:hover { color: var(--ink); }
.seg > button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.seg > button:focus-visible { outline-offset: -3px; }

input[type="range"] { -webkit-appearance: none; appearance: none; background: transparent; width: 9rem; height: 1.5rem; margin: 0; cursor: pointer; }
input[type="range"]::-webkit-slider-runnable-track { height: 2px; background: var(--rule-2); }
input[type="range"]::-moz-range-track { height: 2px; background: var(--rule-2); }
input[type="range"]::-webkit-slider-thumb { -webkit-appearance: none; width: 14px; height: 14px; margin-top: -6px; border-radius: 50%; background: var(--ink); border: 2px solid var(--paper); box-shadow: 0 0 0 1px var(--ink); }
input[type="range"]::-moz-range-thumb { width: 12px; height: 12px; border-radius: 50%; background: var(--ink); border: 2px solid var(--paper); box-shadow: 0 0 0 1px var(--ink); }
input[type="range"]:focus-visible { outline: 3px solid var(--link); outline-offset: 3px; }
select { font: 0.875rem var(--sans); color: var(--ink); background: var(--paper); border: 1px solid var(--rule-2); border-radius: 3px; padding: 0.4rem 0.5rem; }

/* ---------- tables: booktabs ---------- */
table { border-collapse: collapse; width: 100%; font-family: var(--sans); font-size: 0.9rem; line-height: 1.35; margin: 0 0 1.25rem; }
thead th { font-weight: 600; font-size: 0.78rem; letter-spacing: 0.02em; color: var(--ink-2); text-align: left; border-bottom: 1px solid var(--ink); padding: 0.5rem 0.75rem 0.4rem 0; vertical-align: bottom; }
tbody td, tbody th { padding: 0.45rem 0.75rem 0.45rem 0; border-bottom: 1px solid var(--rule); text-align: left; vertical-align: top; font-weight: 400; }
tbody tr:last-child td, tbody tr:last-child th { border-bottom: 1px solid var(--ink); }
td.n, th.n { text-align: right; }

/* ---------- charts (SVG): data ink only ---------- */
.axis line, .axis path { stroke: var(--rule-2); stroke-width: 1; shape-rendering: crispEdges; }
.grid line { stroke: var(--rule); stroke-width: 1; shape-rendering: crispEdges; }
.tick text, .axis text { font-family: var(--sans); font-size: 11.5px; fill: var(--ink-3); }
.axis-title { font-family: var(--sans); font-size: 12px; fill: var(--ink-2); }
.label { font-family: var(--sans); font-size: 12.5px; fill: var(--ink); }
.label.muted { fill: var(--ink-2); }
.annot { font-family: var(--serif); font-style: italic; font-size: 13.5px; fill: var(--ink-2); }
/* a paper-colored outline keeps a label legible where it crosses a gridline or guide */
.halo { paint-order: stroke; stroke: var(--paper); stroke-width: 4px; stroke-linejoin: round; }

/* ---------- top bar: back to the collection, sections, reading progress ---------- */
.topbar { position: sticky; top: 0; z-index: 20; background: var(--paper); border-bottom: 1px solid var(--rule); font-family: var(--sans); font-size: 0.8125rem; }
.topbar-inner { max-width: calc(var(--page) + 3rem); margin: 0 auto; padding: 0 1.5rem; display: flex; align-items: center; gap: 1.25rem; height: 2.75rem; }
.topbar .home { color: var(--ink-2); text-decoration: none; white-space: nowrap; }
.topbar .home:hover { color: var(--ink); }
.topbar .title { color: var(--ink); font-weight: 600; white-space: nowrap; }
.topbar nav { display: flex; gap: 1rem; min-width: 0; overflow-x: auto; scrollbar-width: thin; scrollbar-color: var(--rule-2) var(--paper); margin-left: auto; scroll-padding-inline: 0.25rem; }
.topbar nav a { color: var(--ink-3); text-decoration: none; white-space: nowrap; padding: 0.75rem 0.2rem; }
.topbar nav a:hover, .topbar nav a[aria-current="true"] { color: var(--ink); }
.topbar nav a[aria-current="true"] { text-decoration: underline; text-decoration-thickness: 2px; text-underline-offset: 0.35em; }
.topbar nav a:focus-visible { outline-offset: -3px; }
.progress { position: absolute; left: 0; bottom: -1px; height: 1px; background: var(--ink); width: 0; }

/* ---------- colophon ---------- */
.colophon { margin-top: 5rem; padding-top: 1.25rem; border-top: 1px solid var(--rule); font-size: 0.9rem; color: var(--ink-2); }

/* ---------- narrow screens: notes and captions fall into the column ---------- */
@media (min-width: 62rem) {
  /* minmax(min-content, auto) keeps a scrolling child (overflow-x: auto) from sizing its row to 0,
     which would push the spanning caption's height into empty rows below the graphic */
  .fig:not(.wide) { display: grid; grid-template-columns: var(--text) var(--margin); grid-auto-rows: minmax(min-content, auto); column-gap: var(--gap); max-width: none; align-items: end; }
  .fig:not(.wide) > * { grid-column: 1; }
  .fig:not(.wide) > figcaption { grid-column: 2; grid-row: 1 / span 6; align-self: end; margin: 0; }
}
@media (max-width: 61.99rem) {
  .sidenote, .marginnote { float: none; display: block; width: auto; margin: 0.6rem 0 0.9rem; padding-left: 0.9rem; border-left: 1px solid var(--rule-2); }
}
@media (max-width: 40rem) {
  body { font-size: 1.0625rem; line-height: 1.55; }
  .page, .topbar-inner { padding-left: 1rem; padding-right: 1rem; }
  h1 { margin-top: 3rem; }
  .subtitle { font-size: 1.25rem; }
  .lede { font-size: 1.125rem; }
  h2 { font-size: 1.6rem; margin-top: 3.5rem; }
  .topbar .title { display: none; }
  .btn, .seg > button { min-height: 2.5rem; }
  input[type="range"] { width: 7.5rem; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; scroll-behavior: auto !important; }
}

/* Collection-specific extensions. Entity colors are stable across every lesson:
   blue = selected mechanism; green = selected experts/positive signal;
   red = negative signal; purple = latent state; grey = context. */
:root {
  --ink-3: #666156;
  --text: 54rem;
  --gap: 3rem;
  --margin: 17rem;
}
html { scrollbar-color: var(--rule-2) var(--paper); }
.skip-link { position: absolute; top: -4rem; left: 1rem; z-index: 100; padding: .5rem; background: var(--paper); }
.skip-link:focus { top: .5rem; }
.topbar { background: var(--paper); backdrop-filter: none; }
.topbar-inner { min-width: 0; }
.topbar nav { min-width: 0; mask-image: none; }
.page > .lesson-header { max-width: none; }
.page > h1, .lesson-header h1 { max-width: var(--text); }
.lesson-header .subtitle, .lesson-header .lede { max-width: var(--text); }
.release-note { max-width: var(--text); font: .87rem/1.55 var(--sans); color: var(--ink-2); border-top: 1px solid var(--rule); padding-top: 1rem; margin-top: 1.5rem; }
.release-note span { display: block; }
.figure-title { font: 600 1rem/1.4 var(--sans); margin: 0 0 1rem; }
.widget-graphic svg { min-width: 592px; width: 100%; font: 13px var(--sans); fill: var(--ink); }
.widget-graphic .scroll-x { padding-bottom: .5rem; }
.widget-graphic text.muted { fill: var(--ink-2); }
.widget-graphic text.selected { fill: #1d654e; }
.widget-graphic text.task-label { fill: var(--paper); font-weight: 600; }
.widget-result { font: .88rem/1.5 var(--sans); margin: .6rem 0 0; color: var(--ink-2); }
.fig .controls { align-items: center; }
.fig .control { flex-wrap: wrap; }
.seg { flex-wrap: wrap; }
.flow { list-style: none; padding: 0; margin: 0; counter-reset: stage; }
.flow li { position: relative; border-top: 1px solid var(--rule-2); padding: .75rem 0 .8rem 2.1rem; margin: 0; font: .95rem/1.5 var(--sans); }
.flow li::before { counter-increment: stage; content: counter(stage); position: absolute; left: 0; top: .78rem; font: .84rem var(--mono); color: var(--ink-3); }
.flow strong, .flow span { display: block; }
.flow span { color: var(--ink-2); }
.sources { padding-left: 1.3rem; font-size: 1rem; }
.sources li { padding: .3rem 0 .8rem; }
.sources a { overflow-wrap: anywhere; }
.source-detail { display: block; font: .85rem/1.5 var(--sans); color: var(--ink-2); margin-top: .3rem; }
.read-next { display: grid; grid-template-columns: 1fr 1fr; gap: 1.5rem; padding: 1.5rem 0; border-top: 1px solid var(--rule); }
.read-next a { font-size: 1.15rem; }
.read-next span { display: block; font: .78rem var(--sans); color: var(--ink-3); margin-bottom: .5rem; }
.lesson-links { font: .95rem/1.8 var(--sans); }
.lesson-links a { margin-right: 1rem; display: inline-block; }
#sources, #tutorial-caveats { clear: both; }
.scope-note { font-size: 1rem; color: var(--ink-2); }
.atlas-figure { margin: 2.5rem 0; }
.atlas-figure svg { min-width: 900px; font: 12px var(--sans); }
.reading-paths { border-top: 1px solid var(--ink); }
.reading-path { display: grid; grid-template-columns: 13rem 1fr; gap: 1.5rem; border-bottom: 1px solid var(--rule); padding: 1rem 0; font: .95rem/1.6 var(--sans); }
.reading-path strong { font-family: var(--serif); font-weight: 400; font-size: 1.15rem; }
.reading-path a { display: inline; }
.catalog-controls { align-items: flex-end; margin: 2rem 0 1rem; }
.catalog-controls label { display: grid; gap: .3rem; }
.catalog-controls input[type="search"] { width: min(23rem,100%); border: 1px solid var(--rule-2); border-radius: 3px; background: var(--paper); padding: .55rem .7rem; font: 1rem var(--sans); color: var(--ink); }
.catalog-controls input::placeholder { color: var(--ink-3); }
.catalog { list-style: none; padding: 0; margin: 0; border-top: 1px solid var(--ink); }
.catalog li { display: grid; grid-template-columns: 7rem 1fr 9rem; column-gap: 1.6rem; border-bottom: 1px solid var(--rule); padding: 1.25rem 0; margin: 0; }
.catalog li[hidden] { display: none; }
.catalog time { font: .8rem/1.8 var(--mono); color: var(--ink-3); }
.catalog h3 { font-style: normal; margin: 0 0 .25rem; font-size: 1.5rem; }
.catalog p { font-size: 1rem; margin: 0; }
.catalog .catalog-meta { font: .8rem/1.5 var(--sans); color: var(--ink-3); }
.catalog .catalog-meta span { display: block; }
#match-count, #empty { font: .9rem/1.6 var(--sans); color: var(--ink-2); }
.concepts { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem 3rem; }
.concepts dt { font-weight: 600; margin-bottom: .3rem; }
.concepts dd { margin: 0; font-size: 1rem; color: var(--ink-2); }
.math { display: block; font: .95rem/1.7 var(--mono); overflow-x: auto; padding: .65rem 0; }
/* Keep the wider reading column at intermediate widths; move notes below it
   until the full text + margin grid actually fits. */
@media(max-width: 79.99rem) {
  .page, .topbar-inner { max-width: calc(var(--text) + 3rem); }
  .fig:not(.wide) { display: block; max-width: var(--text); }
  .fig:not(.wide) > figcaption { margin-top: .85rem; }
  .sidenote, .marginnote { float: none; display: block; width: auto; margin: .6rem 0 .9rem; padding-left: .9rem; border-left: 1px solid var(--rule-2); }
}
@media(max-width: 40rem) {
  .catalog li { grid-template-columns: 1fr; gap: .25rem; }
  .catalog .catalog-meta { margin-top: .5rem; }
  .catalog .catalog-meta span { display: inline; margin-right: .8rem; }
  .reading-path { grid-template-columns: 1fr; gap: .3rem; }
  .concepts { grid-template-columns: 1fr; }
  .catalog-controls { display: grid; grid-template-columns: 1fr; }
  .catalog-controls input[type="search"] { width: 100%; }
  .read-next { grid-template-columns: 1fr; }
  .seg > button { padding: .5rem .6rem; }
  .topbar-inner { gap: .8rem; }
}
.topbar .title { max-width: 36%; overflow: hidden; text-overflow: ellipsis; }