/* ROBIN brief — palette lifted from the figures so text and diagrams read as one system. */
:root {
  color-scheme: light;
  --ink: #22313a;
  --slate: #5d6b73;
  --mist: #8a979e;
  --rule: #e3e8ea;
  --paper: #ffffff;
  --paper-2: #f3f6f5;
  --accent: #3f7466;
  --accent-soft: #edf4f1;
  --teal: #2f8592;

  --serif: "Lora", Georgia, serif;
  --display: "Playfair Display", Georgia, serif;
  --mono: "Roboto Mono", ui-monospace, Menlo, monospace;

  --measure: 42rem;
  --wide: 72rem;
  --toc: 14rem;
  --gutter: 16px;
}

*, *::before, *::after { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 2rem; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 400 1.0625rem/1.72 var(--serif);
  font-kerning: normal;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--teal); text-decoration: underline; text-decoration-color: color-mix(in srgb, var(--teal) 35%, transparent); text-underline-offset: 3px; text-decoration-thickness: 1px; transition: text-decoration-color .15s; }
a:hover { text-decoration-color: var(--teal); }

::selection { background: var(--accent-soft); }

/* ------------------------------------------------------------ hero */

.hero {
  padding: clamp(3.5rem, 10vw, 7rem) var(--gutter) clamp(2.5rem, 6vw, 4rem);
  border-bottom: 1px solid var(--rule);
}
.hero-inner { margin: 0 auto; }
.hero-col { width: 100%; max-width: var(--measure); }

.wordmark { display: flex; align-items: flex-end; gap: clamp(1rem, 3vw, 1.75rem); flex-wrap: wrap; }
.wordmark h1 {
  margin: 0;
  font: 400 clamp(4.25rem, 15vw, 8.5rem)/0.82 var(--display);
  color: var(--accent);
  letter-spacing: -0.015em;
}
.acronym {
  margin: 0 0 .35rem;
  font: 400 clamp(1rem, 2.4vw, 1.3rem)/1.25 var(--display);
  color: var(--accent);
}
.acronym strong { font-weight: 600; }

.hero hr { border: 0; border-top: 1px solid var(--accent); margin: 1.6rem 0 1.25rem; opacity: .7; }

.subtitle { margin: 0; font: italic 400 clamp(1.5rem, 4vw, 2.1rem)/1.2 var(--display); }
.lede {
  max-width: 38rem;
  margin: 1.4rem 0 2rem;
  font-size: clamp(1.1rem, 2.2vw, 1.25rem);
  line-height: 1.6;
  color: var(--slate);
}

.button {
  display: inline-flex; align-items: center; gap: .55rem;
  padding: .6rem 1.05rem;
  border: 1px solid var(--accent);
  border-radius: 999px;
  font: 500 .78rem/1 var(--mono);
  letter-spacing: .08em; text-transform: uppercase;
  color: var(--accent); text-decoration: none;
  transition: background .15s, color .15s;
}
.button svg { width: 15px; height: 15px; }
.button:hover { background: var(--accent); color: #fff; }

/* ------------------------------------------------------------ layout */

.layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  max-width: calc(var(--wide) + 2 * var(--gutter));
  margin: 0 auto;
  padding: 0 var(--gutter);
}
main { min-width: 0; padding: 3rem 0 4rem; }

/* Everything shares one left edge: text in a readable column, wide figures out to the full
   width of <main>. */
main > :not(section),
main section > :not(section, figure.wide, .table-wrap) { max-width: var(--measure); margin-left: 0; margin-right: auto; }
main figure.wide, main .table-wrap { max-width: var(--wide); margin-left: 0; }

.toc { display: none; }

@media (min-width: 1100px) {
  .layout {
    grid-template-columns: minmax(0, 1fr) var(--toc);
    column-gap: 4rem;
    max-width: calc(var(--wide) + 4rem + var(--toc) + 2 * var(--gutter));
  }
  main { grid-column: 1; grid-row: 1; }
  .toc {
    grid-column: 2; grid-row: 1;
    display: block;
    position: sticky; top: 0; z-index: 2;  /* above the appendix tone, which bleeds sideways */
    align-self: start;
    max-height: 100vh; overflow-y: auto;
    padding: 3.4rem 0 2rem;
    font-size: .9rem;
  }
  .toc ol { list-style: none; margin: 0; padding: 0; }
  .toc .toc-app { margin-top: 1rem; padding-top: 1rem; border-top: 1px solid var(--rule); }
  .toc ol a {
    display: flex; gap: .7rem;
    padding: .3rem 0 .3rem .8rem;
    border-left: 2px solid transparent;
    color: var(--slate); text-decoration: none; line-height: 1.35;
    transition: color .15s, border-color .15s;
  }
  .toc ol a span { font: 500 .7rem/1.9 var(--mono); color: var(--mist); min-width: 1.3rem; }
  .toc ol a:hover { color: var(--ink); }
  .toc ol a.active { color: var(--accent); border-left-color: var(--accent); }
  .toc ol a.active span { color: var(--accent); }

  /* Sub-entries only show for the section you're reading. */
  .toc li:not(.open) > .toc-sub { display: none; }
  .toc .toc-sub a { padding-left: 2.8rem; font-size: .82rem; }
}

/* ------------------------------------------------------------ type */

.eyebrow {
  margin: 0 0 .35rem;
  font: 500 .72rem/1.4 var(--mono);
  letter-spacing: .14em; text-transform: uppercase;
  color: var(--accent);
}

section.level2 { padding-top: 2.5rem; }
section.appendix { margin-top: 3rem; padding-top: 4rem; border-top: 1px solid var(--rule); }

h2, h3, h4 { position: relative; color: var(--accent); font-family: var(--display); font-weight: 500; text-wrap: balance; }
h2 { font-size: clamp(1.75rem, 4.2vw, 2.3rem); line-height: 1.15; margin-top: 0; margin-bottom: 1.1rem; letter-spacing: -.005em; }
h2 .eyebrow { display: block; margin-bottom: .5rem; font-family: var(--mono); }
section.appendix h2 { font-size: clamp(2rem, 5vw, 2.7rem); }
h3 { font-size: 1.45rem; line-height: 1.25; margin-top: 2.6rem; margin-bottom: .8rem; }
h4 { font-family: var(--serif); font-weight: 700; font-size: 1.02rem; color: var(--ink); margin-top: 2rem; margin-bottom: .5rem; }

h3 .letter {
  display: inline-block; min-width: 1.6em;
  font: 400 1.05em/1 var(--display); color: #7c8f85;
}

.anchor {
  position: absolute; left: -1.3em; bottom: 0;
  padding-right: .4em;
  color: var(--mist); text-decoration: none; font-weight: 400;
  opacity: 0; transition: opacity .15s;
}
h2:hover .anchor, h3:hover .anchor, h4:hover .anchor, .anchor:focus { opacity: 1; }
@media (max-width: 720px) { .anchor { display: none; } }

p { margin-top: 0; margin-bottom: 1.15rem; }
strong { font-weight: 700; }

.pull {
  margin-top: 1.8rem;
  margin-bottom: 1.4rem;
  padding: .2rem 0 .2rem 1.3rem;
  border-left: 2px solid var(--accent);
  font-weight: 600; font-size: 1.12rem; line-height: 1.6;
}
.pull p:last-child { margin-bottom: 0; }

/* ------------------------------------------------------------ lists */

/* One family: bullets and numbers hang in a narrow gutter, aligned to the first line;
   term lists (module rows, definitions) are hairline-ruled rows with the term on the left. */
main ul, main ol { list-style: none; margin: 0 0 1.4rem; padding: 0; }
main li { position: relative; margin: 0 0 .6rem; padding-left: 1.6rem; }
main li:last-child { margin-bottom: 0; }
main li > p { margin-bottom: .5rem; }
main li > p:last-child { margin-bottom: 0; }
main li > :is(ul, ol) { margin: .55rem 0 0; }

main ul > li::before {
  content: ""; position: absolute; left: .35rem; top: .78em;
  width: .36rem; height: .36rem; border-radius: 50%;
  background: color-mix(in srgb, var(--accent) 70%, #fff);
}
main ul ul > li::before { background: none; border: 1px solid var(--accent); }

main ol { counter-reset: r; }
main ol > li { counter-increment: r; padding-left: 2.1rem; margin-bottom: .85rem; }
main ol > li::before {
  content: counter(r); position: absolute; left: 0; top: 0;
  width: 1.4rem; text-align: right;
  font: 400 1.08em/inherit var(--display); font-variant-numeric: lining-nums; color: #7c8f85;
}
main ol > li > strong:first-child { color: var(--ink); }

main dl { margin: 1.2rem 0 1.6rem; padding: 0; font: 400 1.02rem/1.6 var(--sans); }
main dt { margin: 0; font-weight: 650; color: var(--accent); }
main dd { margin: .1rem 0 1rem 1.4rem; color: var(--ink); }
main dd:last-child { margin-bottom: 0; }
main dd p { margin: 0; }

.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(12rem, 1fr)); gap: .8rem; margin-bottom: 1.4rem; }
.card { padding: .9rem 1.1rem; border: 1px solid var(--rule); border-radius: 6px; }
.card p:last-child { margin: 0; font-size: .97rem; line-height: 1.55; }

/* ------------------------------------------------------------ callouts */

.callout {
  margin-bottom: 1.6rem;
  padding: 1.05rem 1.3rem;
  border-left: 3px solid var(--accent);
  border-radius: 0 6px 6px 0;
  background: var(--accent-soft);
  font-size: .97rem; line-height: 1.65;
}
.callout p:last-child { margin-bottom: 0; }
.callout-title { margin-bottom: .35rem; font: 500 .72rem/1.4 var(--mono); letter-spacing: .14em; text-transform: uppercase; color: var(--accent); }

/* ------------------------------------------------------------ tables */

/* Small sans text, quiet uppercase labels, one firm rule under the header, hairlines between rows. */
.table-wrap { margin: 1.6rem 0 2rem; overflow-x: auto; -webkit-overflow-scrolling: touch; }
.table-wrap table { width: 100%; border-collapse: collapse; font: 400 .9rem/1.45 var(--sans); color: var(--ink); }
.table-wrap th {
  padding: 0 .9rem .55rem 0;
  font: 600 .7rem/1.3 var(--sans); letter-spacing: .08em; text-transform: uppercase; color: var(--slate);
  text-align: left; vertical-align: bottom; white-space: nowrap;
  border-bottom: 1px solid var(--slate);
}
.table-wrap td { padding: .6rem .9rem .6rem 0; vertical-align: top; border-bottom: 1px solid var(--rule); }
.table-wrap :is(th, td):last-child { padding-right: 0; }
.table-wrap td:first-child { font-weight: 600; }
.table-wrap td code { font-size: .8em; white-space: nowrap; }
.table-wrap caption { caption-side: bottom; padding-top: .7rem; text-align: left; font: 400 .85rem/1.5 var(--sans); color: var(--slate); }

/* ------------------------------------------------------------ code */

code {
  font: 400 .84em/1 var(--mono);
  color: var(--teal);
  background: var(--paper-2);
  padding: .14em .36em;
  border-radius: 3px;
  overflow-wrap: anywhere;
}
pre {
  position: relative;
  margin-bottom: 1.6rem;
  padding: 1rem 1.25rem;
  overflow-x: auto;
  background: var(--paper-2);
  border-left: 3px solid var(--teal);
  border-radius: 0 6px 6px 0;
}
pre code { padding: 0; background: none; font-size: .84rem; line-height: 1.75; color: var(--ink); overflow-wrap: normal; white-space: pre; }

.copy {
  position: absolute; top: .55rem; right: .55rem;
  padding: .25rem .55rem;
  border: 1px solid var(--rule); border-radius: 4px;
  background: #fff; color: var(--slate);
  font: 500 .65rem/1.2 var(--mono); letter-spacing: .08em; text-transform: uppercase;
  cursor: pointer; opacity: 0; transition: opacity .15s;
}
pre:hover .copy, .copy:focus { opacity: 1; }
@media (hover: none) { .copy { opacity: 1; } }

/* ------------------------------------------------------------ figures */

/* The diagrams already sit on white, so they go straight onto the page with no frame. */
figure { margin: 2.6rem auto 2.8rem; }
figure img { display: block; width: 100%; height: auto; cursor: zoom-in; }
figcaption {
  max-width: var(--measure);
  margin: 1rem 0 0;
  padding-top: .7rem;
  border-top: 1px solid var(--rule);
  font-size: .88rem; line-height: 1.5; color: var(--slate);
}
figcaption span {
  margin-right: .7rem;
  font: 500 .7rem/1 var(--mono); letter-spacing: .12em; text-transform: uppercase; color: var(--accent);
}

dialog#lightbox {
  width: min(96vw, 1800px); max-width: none; max-height: 94vh;
  padding: 1.25rem; border: 0; border-radius: 10px;
  background: #fff;
  box-shadow: 0 30px 80px -20px rgba(0,0,0,.4);
  overflow: auto;
}
dialog#lightbox::backdrop { background: rgba(34, 49, 58, .55); backdrop-filter: blur(3px); }
dialog#lightbox .lb-body img, dialog#lightbox .lb-body svg { display: block; width: 100%; height: auto; }
dialog#lightbox .lb-caption { margin: .9rem 0 0; font-size: .9rem; color: var(--slate); }
dialog#lightbox .lb-caption span { margin-right: .7rem; font: 500 .7rem/1 var(--mono); letter-spacing: .12em; text-transform: uppercase; color: var(--accent); }
dialog#lightbox .close {
  position: sticky; top: 0; float: right;
  width: 2rem; height: 2rem; margin: -.4rem -.4rem 0 0;
  border: 1px solid var(--rule); border-radius: 50%;
  background: #fff; color: var(--slate); font-size: 1.2rem; line-height: 1; cursor: pointer;
}

/* ------------------------------------------------------------ footer */

footer {
  display: flex; justify-content: space-between; flex-wrap: wrap; gap: 1rem;
  max-width: calc(var(--wide) + 4rem + var(--toc) + 2 * var(--gutter));
  margin: 0 auto; padding: 2rem var(--gutter) 3rem;
  border-top: 1px solid var(--rule);
  font: 400 .75rem/1.4 var(--mono); letter-spacing: .06em; color: var(--mist);
}
footer p { margin: 0; }
footer .mark { font: 500 1rem/1 var(--display); color: var(--accent); letter-spacing: 0; }
footer a { color: var(--slate); }

@media print {
  .comments-btn { display: none !important; }
  hypothesis-highlight { background: none !important; box-shadow: none !important; }
  .toc, .button, .copy, footer a { display: none !important; }
}

/* Line the hero up with the reading column when the contents rail is showing. */
@media (min-width: 1100px) {
  .hero-inner {
    display: grid;
    grid-template-columns: minmax(0, 1fr) var(--toc);
    column-gap: 4rem;
    max-width: calc(var(--wide) + 4rem + var(--toc));
  }
  .hero-col { grid-column: 1; }
}

/* ------------------------------------------------------------ interactive figures */

.ifig-wrap, #lightbox .lb-body { position: relative; }
svg.ifig { display: block; width: 100%; height: auto; }
svg.ifig .leaf { transition: opacity .2s ease; }
svg.ifig.focus .leaf:not(.on) { opacity: .14; }
svg.ifig .veil { fill: #fff; opacity: 0; pointer-events: none; transition: opacity .2s ease; }
svg.ifig.veiled .veil { opacity: .86; }
svg.ifig .lift { pointer-events: none; }
svg.ifig .hit rect { fill: transparent; }
figure svg.ifig { cursor: zoom-in; }
#lightbox svg.ifig { cursor: default; }
svg.ifig .hit:focus { outline: none; }
svg.ifig .hit:focus-visible rect { stroke: var(--accent); stroke-width: 3; stroke-dasharray: 8 6; }
.ftip {
  position: absolute; z-index: 5;
  width: min(22rem, calc(100% - 16px));
  padding: .8rem 1rem .9rem;
  border-left: 3px solid var(--tip, var(--accent));
  border-radius: 0 6px 6px 0;
  background: color-mix(in srgb, var(--tip, transparent) 7%, #fff);
  box-shadow: 0 0 0 1px var(--rule), 0 12px 32px -12px rgba(34, 49, 58, .35);
  font-size: .9rem; line-height: 1.5; color: var(--ink);
  pointer-events: none;
}
.ftip strong { display: block; margin-bottom: .2rem; font: 500 .72rem/1.4 var(--mono); letter-spacing: .12em; text-transform: uppercase; color: var(--tip-ink, var(--accent)); }
.fhint { color: var(--mist); font-style: italic; }

/* Editorial refresh: clear reading paths, deliberate whitespace, and quiet UI. */
:root {
  --sans: "Source Sans 3", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --gutter: clamp(22px, 4.5vw, 76px);
  --wide: 68rem;
  --toc: 12rem;
}
.hero { padding-top: clamp(3rem, 6vw, 6rem); padding-bottom: 3.5rem; }
.hero-inner {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(19rem, .85fr);
  gap: clamp(3rem, 6vw, 7rem);
  align-items: center;
  max-width: 82rem;
}
.hero-col { max-width: 42rem; }
.wordmark h1 { font-size: clamp(4.5rem, 8vw, 7.5rem); }
.acronym { font-size: clamp(.95rem, 1.5vw, 1.2rem); }
.hero hr { margin-top: 1.8rem; border-color: var(--rule); opacity: 1; }
.subtitle { font-size: clamp(1.6rem, 2.5vw, 2.1rem); }
.lede { font-size: 1.12rem; line-height: 1.75; margin-bottom: 1.8rem; }
.hero-actions { display: flex; flex-wrap: wrap; gap: .75rem; }
.button {
  min-height: 46px; padding: .8rem 1.1rem; border-radius: 7px;
  font: 700 .88rem/1.2 var(--sans); letter-spacing: 0; text-transform: none;
}
.button-primary { background: var(--accent); color: white; }
.button-primary:hover { background: #2e594e; }
.button-primary span { margin-left: .6rem; }
.hero-routes { display: flex; flex-wrap: wrap; gap: .6rem 1.5rem; margin-top: 1.8rem; }
.hero-routes a, .map-link { font: 600 .8rem/1.5 var(--sans); text-decoration: none; color: var(--slate); }
.hero-routes a span { margin-left: .3rem; color: var(--accent); }
.hero-routes a:hover, .map-link:hover { color: var(--accent); text-decoration: underline; }
.hero-map {
  padding: clamp(1.4rem, 3vw, 2.5rem); border: 1px solid #dce6e1; border-radius: 18px;
  background: linear-gradient(145deg, #f8faf8, #edf3f0); text-align: center;
}
.hero-map > .eyebrow { margin-bottom: 2rem; font-size: .64rem; }
.map-ports { display: flex; justify-content: center; gap: .5rem; }
.map-ports span {
  flex: 1; padding: .65rem .35rem; border: 1px solid #d8e2dc; border-radius: 6px;
  background: #ffffffb3; font: 600 .75rem/1.3 var(--sans); color: #50665d;
}
.map-ports-bottom { max-width: 80%; margin: auto; }
.map-connector { height: 26px; width: 1px; background: #9eb7ac; margin: auto; }
.map-core { padding: 1.65rem 1rem; border-radius: 10px; background: #284e43; color: white; box-shadow: 0 14px 30px -20px #193e32a6; }
.map-label { font: 500 .64rem/1 var(--mono); letter-spacing: .15em; color: #c4d8cb; }
.map-core p { font: 400 clamp(2rem, 3vw, 2.75rem)/1.15 var(--display); margin: .8rem 0 1rem; }
.map-detail { font: 400 .71rem/1.5 var(--sans); color: #d3e2d9; }
.map-caption { font: 400 .8rem/1.6 var(--sans); color: var(--slate); margin: 1.5rem 0 .8rem; }
.map-link { color: var(--accent); }
.layout { max-width: calc(82rem + 2 * var(--gutter)); }
main { padding-top: 3.5rem; }
.toc, figcaption, .lb-caption, .callout, main dl, .card, .ftip { font-family: var(--sans); }
.toc { font-size: .83rem; }
.toc ol a { padding-top: .45rem; padding-bottom: .45rem; }
.callout { border-left-width: 2px; padding: 1.2rem 1.4rem; background: #f2f6f3; }
.callout-title { font-family: var(--sans); letter-spacing: .08em; font-weight: 700; }
section.level2 { padding-top: 4rem; }
section.level2 + section.level2 { margin-top: 2rem; border-top: 1px solid var(--rule); }
h2 { font-size: clamp(1.8rem, 3vw, 2.5rem); letter-spacing: -.025em; }
h3 { font-family: var(--sans); font-weight: 700; font-size: 1.35rem; letter-spacing: -.015em; }
h4 { font-family: var(--sans); }
.section-takeaway { font: 400 1.0625rem/1.65 var(--serif); color: var(--slate); margin-top: -.25rem; margin-bottom: 1.35rem; }
main section.level2 > p.section-takeaway {
  margin-left: calc(clamp(1.8rem, 3vw, 2.5rem) * 1.4);
  max-width: calc(var(--measure) - clamp(1.8rem, 3vw, 2.5rem) * 1.4);
}
figure { margin-top: 3rem; margin-bottom: 3.2rem; }
figcaption { font-size: .82rem; line-height: 1.65; }
section.appendix { padding-top: 3.5rem; border-top: 2px solid #bdd0c5; }
section.appendix > h2 .eyebrow { color: var(--slate); }
.appendix-guide { margin: 1.5rem 0 2rem; padding: 1.4rem; border: 1px solid #dce6e1; border-radius: 9px; background: #f6f8f6; font: 400 .95rem/1.6 var(--sans); }
.appendix-guide p { margin: .5rem 0 1rem; }
.appendix-guide nav { display: flex; flex-wrap: wrap; gap: .6rem 1.4rem; }
.appendix-guide a { font-size: .8rem; font-weight: 700; }
a:focus-visible, button:focus-visible { outline: 2px solid var(--accent); outline-offset: 5px; }
@media (min-width: 1100px) {
  .layout { column-gap: clamp(3rem, 5vw, 5rem); }
  .hero-inner { grid-template-columns: minmax(0, 1.35fr) minmax(19rem, .85fr); }
}
@media (max-width: 850px) {
  .hero-inner { grid-template-columns: 1fr; gap: 2.5rem; }
  .hero-col { max-width: 100%; }
  .hero-map { max-width: 32rem; width: 100%; }
  .hero-routes { gap: .8rem 1.2rem; }
  section.level2 { padding-top: 2.8rem; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition: none !important; }
}

/* Plain labels and section numerals that belong to the heading. */
.eyebrow, .callout-title, .ftip strong,
figcaption span, dialog#lightbox .lb-caption span {
  font-family: var(--sans);
  font-weight: 600;
  text-transform: none;
  letter-spacing: 0;
}
.eyebrow { font-size: .84rem; line-height: 1.5; color: var(--slate); }
.callout-title { font-size: .88rem; }
.ftip strong { font-size: .88rem; }
figcaption span, dialog#lightbox .lb-caption span { font-size: .82rem; }
section.level2 > h2 {
  display: grid;
  grid-template-columns: 1.1em minmax(0, 1fr);
  column-gap: .3em;
  align-items: baseline;
}
section.level2 > h2 .eyebrow {
  display: block; margin: 0;
  font: 400 .8em/1.15 var(--display);
  letter-spacing: -.03em;
  color: #7c8f85;
}
section.appendix > h2 { display: block; }
section.appendix > h2 .eyebrow {
  margin-bottom: .65rem;
  font: 400 1rem/1.4 var(--serif);
  letter-spacing: 0;
  color: var(--slate);
}
.toc ol a span { font: 400 .85rem/1.35 var(--serif); color: var(--slate); }

/* ---------- comments (Hypothesis) ---------- */
:root {
  --hypothesis-highlight-color: color-mix(in srgb, var(--accent) 13%, transparent);
  --hypothesis-highlight-secondColor: color-mix(in srgb, var(--accent) 20%, transparent);
  --hypothesis-highlight-thirdColor: color-mix(in srgb, var(--accent) 26%, transparent);
  --hypothesis-highlight-focused-color: color-mix(in srgb, var(--teal) 24%, transparent);
}
hypothesis-highlight {
  box-shadow: inset 0 -1.5px color-mix(in srgb, var(--accent) 55%, transparent);
  border-radius: 2px;
  transition: background-color .15s;
}
.comments-btn {
  position: fixed; right: 1.25rem; bottom: 1.25rem; z-index: 20;
  display: inline-flex; align-items: center; gap: .45rem;
  padding: .55rem .95rem .55rem .8rem;
  font: 600 .85rem/1 var(--sans); color: var(--accent);
  background: var(--paper); border: 1px solid var(--rule); border-radius: 999px;
  box-shadow: 0 1px 2px rgb(34 49 58 / .06), 0 4px 14px rgb(34 49 58 / .08);
  cursor: pointer; transition: border-color .15s, box-shadow .15s;
}
.comments-btn:hover { border-color: color-mix(in srgb, var(--accent) 45%, var(--rule)); box-shadow: 0 1px 2px rgb(34 49 58 / .08), 0 6px 18px rgb(34 49 58 / .12); }
.comments-btn svg { width: 1rem; height: 1rem; fill: none; stroke: currentColor; stroke-width: 1.5; stroke-linejoin: round; }
.comments-btn .count, .toc-comments .count { min-width: 1.35rem; padding: .2rem .4rem; border-radius: 999px; background: var(--accent-soft); font-size: .75rem; text-align: center; }
.count:empty, .count[data-zero] { display: none; }
.toc-comments { display: none; }
@media (min-width: 1100px) {
  .comments-btn { display: none; }
  .toc-comments {
    display: flex; align-items: center; gap: .5rem; width: 100%;
    margin-top: 1rem; padding: 1rem 0 0 .8rem;
    border: 0; border-top: 1px solid var(--rule); background: none;
    font: 600 .85rem/1 var(--sans); color: var(--accent); cursor: pointer; text-align: left;
  }
  .toc-comments::before {
    content: ""; width: 1rem; height: 1rem; background: currentColor;
    -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'%3E%3Cpath d='M4 4h12a1.5 1.5 0 0 1 1.5 1.5v7A1.5 1.5 0 0 1 16 14H9l-4 3v-3H4a1.5 1.5 0 0 1-1.5-1.5v-7A1.5 1.5 0 0 1 4 4z' fill='none' stroke='black' stroke-width='1.5' stroke-linejoin='round'/%3E%3C/svg%3E") center / contain no-repeat;
            mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'%3E%3Cpath d='M4 4h12a1.5 1.5 0 0 1 1.5 1.5v7A1.5 1.5 0 0 1 16 14H9l-4 3v-3H4a1.5 1.5 0 0 1-1.5-1.5v-7A1.5 1.5 0 0 1 4 4z' fill='none' stroke='black' stroke-width='1.5' stroke-linejoin='round'/%3E%3C/svg%3E") center / contain no-repeat;
  }
  .toc-comments:hover { color: var(--ink); }
}
body.h-open .comments-btn { opacity: 0; pointer-events: none; }

/* ---------- back to top: at the foot of the sticky contents on desktop, floating on phones ---------- */
.to-top {
  position: fixed; right: 1.25rem; bottom: 4.6rem; z-index: 20;
  display: inline-flex; align-items: center; justify-content: center;
  width: 2.5rem; height: 2.5rem;
  font: 600 .85rem/1 var(--sans); color: var(--accent); text-decoration: none;
  background: var(--paper); border: 1px solid var(--rule); border-radius: 999px;
  box-shadow: 0 1px 2px rgb(34 49 58 / .06), 0 4px 14px rgb(34 49 58 / .08);
  opacity: 0; pointer-events: none; transition: opacity .2s, color .15s;
}
.to-top::before { content: "↑"; font-size: 1rem; }
.to-top span { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); }
body.scrolled .to-top { opacity: 1; pointer-events: auto; }
body.h-open .to-top { opacity: 0; pointer-events: none; }
.to-top:hover { color: var(--ink); }
@media (min-width: 1100px) {
  .toc { height: 100vh; display: flex; flex-direction: column; }
  .to-top {
    position: static; margin-top: auto; align-self: flex-start;
    width: auto; height: auto; gap: .5rem;
    padding: 1.5rem 0 0 .8rem;
    background: none; border: 0; box-shadow: none;
  }
  .to-top span { position: static; width: auto; height: auto; overflow: visible; clip-path: none; }
}

/* ---------- appendices: a faint warm paper tone marks them as reference, not the main text ---------- */
:root { --appendix: #f7f6f1; }
section.appendix {
  position: relative;
  display: flow-root;   /* keep the last child's margin inside, so no white seam between appendices */
  /* Paint the tone edge to edge without changing the layout. */
  box-shadow: 0 0 0 100vmax var(--appendix);
  clip-path: inset(0 -100vmax);
  background: var(--appendix);
}
section.appendix:first-of-type, section:not(.appendix) + section.appendix { margin-top: 4rem; border-top: 0; }
section.appendix + section.appendix { margin-top: 0; padding-top: 5rem; border-top: 0; }
section.appendix:last-child { padding-bottom: 4rem; }
main:has(> section.appendix:last-child) { padding-bottom: 0; }
/* Figures sit straight on the tone: drop any painted white background, and fade to the tone, not white. */
section.appendix svg.ifig .bg { fill: transparent; }
section.appendix svg.ifig .veil { fill: var(--appendix); }
/* Code stays on white cards so it reads crisply. */
section.appendix pre { background: #fff; box-shadow: 0 0 0 1px #e7e5dc; }
section.appendix :not(pre) > code { background: #eeece4; }
section.appendix .callout { background: #fff; }