:root {
  color-scheme: light;
  --ink: #252525;
  --muted: #6f777d;
  --paper: #fff;
  --nav: #2b3440;
  --nav-rule: #3c4c5e;
  --nav-text: #7fa4bb;
  --nav-muted: #536d83;
  --rule: #dce7ec;
  --link: #1682b6;
  --link-dark: #075f88;
  --code-bg: #faf8f4;
  --code-ink: #686866;
  --note-blue: #eef4f7;
  --note-green: #f4f7ef;
  --optional: #a76c27;
  --focus: #ffbd3e;
  --serif: "IBM Plex Serif", Georgia, serif;
  --display: "IBM Plex Serif", Georgia, serif;
  --sans: "IBM Plex Sans", "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: "IBM Plex Mono", "SFMono-Regular", Consolas, monospace;
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.55;
}

html[data-typeface="plex"] {
  --serif: "IBM Plex Serif", Georgia, serif;
  --display: "IBM Plex Serif", Georgia, serif;
  --sans: "IBM Plex Sans", "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: "IBM Plex Mono", "SFMono-Regular", Consolas, monospace;
}

html[data-typeface="google-sans"] {
  --serif: "Google Sans Flex", "Segoe UI", Helvetica, Arial, sans-serif;
  --display: "Google Sans Flex", "Segoe UI", Helvetica, Arial, sans-serif;
  --sans: "Google Sans Flex", "Segoe UI", Helvetica, Arial, sans-serif;
  --mono: "Google Sans Code", "SFMono-Regular", Consolas, monospace;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  min-width: 18rem;
  margin: 0;
  color: var(--ink);
  background: var(--paper);
}

a {
  color: var(--link);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color 160ms ease, border-color 160ms ease;
}

a:hover {
  color: var(--link-dark);
  border-bottom-color: var(--rule);
}

a:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

img,
svg {
  max-width: 100%;
  height: auto;
}

.skip-link {
  position: fixed;
  z-index: 20;
  top: 0.5rem;
  left: 0.5rem;
  padding: 0.45rem 0.75rem;
  color: #1d2730;
  background: var(--focus);
  border: 0;
  transform: translateY(-180%);
}

.skip-link:focus {
  transform: translateY(0);
}

/* The desktop rail is deliberately book navigation, not a site header. */
.book-nav {
  position: fixed;
  inset: 0 auto 0 0;
  width: 20rem;
  overflow-y: auto;
  color: var(--nav-text);
  background: var(--nav);
  font: 300 0.82rem/1.5 var(--sans);
}

.book-nav a {
  color: var(--nav-text);
  border: 0;
}

.book-nav a:hover,
.book-nav a[aria-current] {
  color: #edf4f7;
}

.wordmark {
  display: block;
  padding: 3.1rem 2.7rem 1.4rem;
  color: #edf4f7;
  border: 0;
}

.wordmark strong {
  display: block;
  font: 600 2rem/0.95 var(--display);
  letter-spacing: -0.035em;
}

.wordmark span {
  display: block;
  margin-top: 0.48rem;
  color: var(--nav-text);
  font: 500 0.67rem/1.2 var(--sans);
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.book-nav .nav-contents {
  margin: 1rem 2.7rem 2.5rem;
}

.book-nav .part-label {
  margin: 0 0 0.35rem;
  color: var(--nav-muted);
  font-size: 0.67rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.book-nav h2 {
  margin: 0;
  color: var(--nav-text);
  font: 400 1.02rem/1.35 var(--sans);
}

.book-nav h2 small {
  float: right;
  color: var(--nav-muted);
  font-size: 0.85rem;
}

.book-nav ul {
  margin: 0.6rem 0 0;
  padding: 0.55rem 0 0.4rem;
  border-top: 1px solid var(--nav-rule);
  border-bottom: 1px solid var(--nav-rule);
  list-style: none;
}

.book-nav li {
  margin: 0 0 0.38rem;
}

.book-nav li a {
  display: grid;
  grid-template-columns: 2.6rem 1fr;
  gap: 0.35rem;
}

.book-nav li small {
  color: var(--nav-muted);
  font-size: 0.74rem;
  text-align: right;
}

.book-nav li.divider {
  height: 1px;
  margin: 0.6rem 0;
  background: var(--nav-rule);
}

.book-nav li.optional-link a {
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.book-nav .prev-next {
  display: flex;
  justify-content: space-between;
  margin-top: 0.7rem;
  font-size: 0.66rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.book-nav-mobile {
  display: none;
  min-height: 3.25rem;
  align-items: center;
  justify-content: space-between;
  padding: 0.35rem 1.2rem;
  color: var(--nav-text);
  background: var(--nav);
  font-family: var(--sans);
}

.book-nav-mobile a {
  color: var(--nav-text);
  border: 0;
}

.book-nav-mobile .mobile-title {
  color: #edf4f7;
  font: 600 1.05rem var(--display);
}

.book-nav-mobile .mobile-arrow {
  min-width: 2.2rem;
  font-size: 1.6rem;
  text-align: center;
}

.page {
  position: relative;
  width: 50.7rem;
  margin: 0 auto 0 23rem;
}

.chapter,
.contents-page {
  position: relative;
  width: 32rem;
}

.contents-page {
  width: 46rem;
}

.chapter-number {
  position: absolute;
  z-index: 0;
  top: 2.2rem;
  left: 34.7rem;
  color: var(--rule);
  font: 300 6rem/1 var(--sans);
  letter-spacing: -0.08em;
}

.chapter-header,
.contents-header {
  position: relative;
  z-index: 1;
  padding: 5.8rem 0 1rem;
}

.chapter-header h1,
.contents-header h1 {
  max-width: 12em;
  margin: 0;
  font: 400 clamp(2.55rem, 5vw, 3rem)/1 var(--display);
  letter-spacing: -0.035em;
}

.chapter-header .optional-kicker,
.contents-header .kicker {
  margin: 0 0 0.4rem;
  color: var(--optional);
  font: 600 0.7rem/1.4 var(--sans);
  letter-spacing: 0.13em;
  text-transform: uppercase;
}

.contents-header .deck {
  margin: 1.1rem 0 0;
  color: #547e9c;
  font: italic 1.25rem/1.5 var(--serif);
}

.chapter p,
.contents-page p {
  margin: 1.35rem 0;
}

.chapter h2 {
  position: relative;
  margin: 3.8rem 0 0;
  font: 600 1.72rem/1.25 var(--display);
}

.chapter h3 {
  margin: 3rem 0 0;
  font: italic 1.35rem/1.3 var(--display);
}

.chapter h2 a,
.chapter h3 a {
  color: var(--ink);
  border: 0;
}

.chapter h2 a::before,
.chapter h3 a::before {
  position: absolute;
  left: -2rem;
  width: 1.5rem;
  color: transparent;
  content: "§";
  text-align: center;
  transition: color 160ms ease;
}

.chapter h2 a:hover::before,
.chapter h2 a:focus-visible::before,
.chapter h3 a:hover::before,
.chapter h3 a:focus-visible::before {
  color: var(--rule);
}

.section-number {
  float: right;
  margin: 0.35rem 0 0 1rem;
  color: var(--muted);
  font: 700 0.68rem/1 var(--sans);
  letter-spacing: 0.06em;
}

.chapter ol,
.chapter ul,
.contents-page ol,
.contents-page ul {
  margin: 1.35rem 0;
  padding-left: 1.35rem;
}

.chapter li + li {
  margin-top: 0.35rem;
}

.chapter table {
  width: 100%;
  margin: 1.6rem 0;
  border-collapse: collapse;
  font: 0.78rem/1.45 var(--sans);
}

.chapter th,
.chapter td {
  padding: 0.55rem 0.65rem;
  border: 1px solid var(--rule);
  text-align: left;
  vertical-align: top;
}

.chapter th {
  color: #40596b;
  background: var(--note-blue);
  font-weight: 650;
}

.chapter hr {
  margin: 3rem 0;
  border: 0;
  border-top: 1px solid var(--rule);
}

.chapter-note,
.design-note {
  margin: 1.6rem -0.7rem;
  padding: 0.75rem 0.7rem;
  color: #444;
  background: var(--note-blue);
  border-radius: 3px;
  font: 400 0.9rem/1.5 var(--sans);
}

.design-note {
  background: var(--note-green);
}

.chapter-note h2,
.design-note h2 {
  margin: 0 0 0.4rem;
  font: 650 0.78rem/1.4 var(--sans);
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.chapter-note ul,
.design-note ul {
  margin: 0.45rem 0 0;
}

.chapter-note > :last-child,
.design-note > :last-child {
  margin-bottom: 0;
}

blockquote.design-note {
  margin: 1.8rem -0.7rem;
  padding: 0.8rem 1rem;
  color: #444;
}

blockquote.design-note::before,
blockquote.design-note::after {
  display: none;
}

blockquote.design-note p {
  margin: 0 !important;
  font: 500 0.92rem/1.55 var(--sans);
}

.margin-note {
  position: absolute;
  right: -18.7rem;
  width: 16rem;
  margin-top: 0.25rem;
  padding-top: 0.35rem;
  color: #4d555b;
  border-top: 1px solid var(--rule);
  font: 400 0.8rem/1.45 var(--serif);
}

.margin-note p {
  margin: 0.45rem 0;
}

code,
kbd {
  color: var(--code-ink);
  font: 0.86em var(--mono);
}

:not(pre) > code {
  padding: 0.08rem 0.18rem;
  white-space: nowrap;
}

.code-block {
  position: relative;
  margin: 1.35rem -0.7rem;
  padding: 0.7rem;
  color: var(--code-ink);
  background: var(--code-bg);
  border-radius: 3px;
}

pre {
  margin: 0;
  overflow-x: auto;
  font: 0.72rem/1.55 var(--mono);
  tab-size: 4;
}

pre code {
  color: inherit;
  font: inherit;
  white-space: pre;
}

.source-file {
  position: absolute;
  top: 0.65rem;
  right: -18.7rem;
  width: 16rem;
  color: #aaa9a7;
  font: 0.61rem/1.4 var(--mono);
}

.source-file::before {
  margin-right: 0.45rem;
  color: #d6d4d0;
  content: "←";
}

.source-file a {
  color: #8a8987;
  border-bottom-color: var(--rule);
}

.stack-model {
  width: 50.7rem;
  margin: 2rem 0;
}

.stack-model img {
  display: block;
  width: 100%;
}

.stack-model figcaption {
  width: 32rem;
  margin-top: 0.55rem;
  color: var(--muted);
  font: 0.76rem/1.45 var(--sans);
}

.chapter-figure {
  width: 50.7rem;
  margin: 2rem 0;
}

.chapter-figure img {
  display: block;
  width: 100%;
  max-height: 36rem;
}

.chapter-figure figcaption {
  width: 32rem;
  margin-top: 0.55rem;
  color: var(--muted);
  font: 0.76rem/1.45 var(--sans);
}

blockquote {
  position: relative;
  margin: 1.8rem 0;
  color: #5985a6;
}

blockquote::before,
blockquote::after {
  position: absolute;
  top: -1.4rem;
  color: var(--rule);
  font: italic 4rem var(--display);
}

blockquote::before {
  left: -0.25rem;
  content: "“";
}

blockquote::after {
  right: 0.5rem;
  content: "”";
}

blockquote p {
  margin-inline: 2.7rem !important;
  font: italic 1.25rem/1.5 var(--serif);
}

blockquote.epigraph {
  margin: 1.8rem 0 3.2rem;
}

blockquote.epigraph p:last-child {
  margin-top: 0.65rem !important;
  color: var(--muted);
  font: 500 0.72rem/1.4 var(--sans);
  font-style: normal;
  letter-spacing: 0.02em;
  text-align: right;
}

blockquote.epigraph cite {
  font-style: normal;
}

.contents-header {
  padding-bottom: 2.2rem;
}

.contents-header h1 {
  font-size: 3.5rem;
}

.contents-page .ornament {
  margin: 1rem 0;
  color: var(--rule);
  font-size: 1.8rem;
  text-align: center;
}

.contents-group {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 3rem;
  margin-top: 1.5rem;
}

.contents-group-complete {
  grid-template-columns: minmax(0, 1.55fr) minmax(13rem, 0.75fr);
}

.contents-group h2 {
  margin: 0 0 0.55rem;
  font: 650 0.92rem/1.4 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.contents-list {
  margin: 0 !important;
  padding: 0 !important;
  list-style: none;
}

.contents-list li {
  display: grid;
  grid-template-columns: 2.2rem 1fr;
  gap: 0.4rem;
  padding: 0.7rem 0;
  border-top: 1px solid var(--rule);
  font-family: var(--sans);
}

.contents-list .num {
  color: var(--nav-text);
  font-size: 0.76rem;
  text-align: right;
}

.contents-list strong {
  display: block;
  font-size: 0.98rem;
  font-weight: 600;
}

.contents-list p {
  margin: 0.18rem 0 0;
  color: var(--muted);
  font: 0.75rem/1.45 var(--sans);
}

.contents-list .optional-label {
  display: block;
  margin-bottom: 0.1rem;
  color: var(--optional);
  font-size: 0.62rem;
  font-weight: 700;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.prototype-note {
  margin-top: 2.7rem;
  padding: 0.8rem 1rem;
  color: #4d555b;
  background: var(--note-green);
  border-radius: 3px;
  font: 0.82rem/1.5 var(--sans);
}

.prototype-note h2 {
  margin: 0 0 0.25rem;
  font: 650 0.72rem/1.4 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.prototype-note p {
  margin: 0;
}

.archive-note {
  margin: 1.2rem 0 2.5rem;
  padding: 0.85rem 1rem;
  color: #4d555b;
  background: var(--note-green);
  border-radius: 3px;
  font: 0.82rem/1.5 var(--sans);
}

.archive-note strong {
  color: #314956;
}

.lab-contents > section {
  margin-top: 2.6rem;
}

.lab-contents > section > h2 {
  margin: 0 0 0.55rem;
  font: 650 0.92rem/1.4 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.lab-list li {
  grid-template-columns: 3.7rem 1fr;
}

.home-labs {
  margin-top: 2.4rem;
  padding: 0.9rem 1rem;
  background: var(--note-green);
  border-radius: 3px;
}

.home-labs h2 {
  margin: 0;
  color: #40596b;
  font: 650 0.78rem/1.4 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.home-labs p {
  margin: 0.25rem 0 0;
  font: 0.88rem/1.45 var(--sans);
}

.lab-page .lab-callout {
  margin: 1.6rem -0.7rem;
  padding: 0.8rem 1rem;
  color: #444;
  background: var(--note-blue);
  border-radius: 3px;
  font: 0.9rem/1.55 var(--sans);
}

.lab-page .lab-callout .lab-callout {
  margin: 0.6rem 0;
  padding: 0 0 0 0.8rem;
  background: transparent;
  border-left: 2px solid var(--rule);
}

.lab-page .lab-callout > :first-child {
  margin-top: 0;
}

.lab-page .lab-callout > :last-child {
  margin-bottom: 0;
}

.lab-page .lab-callout h2,
.lab-page .lab-callout h3 {
  margin-top: 0;
  font: 650 0.82rem/1.4 var(--sans);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.lab-page img {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 1.6rem auto;
}

.lab-page math[display="block"] {
  display: block;
  max-width: 100%;
  margin: 1.4rem 0;
  overflow-x: auto;
}

.example-index {
  margin-inline: auto;
}

.file-list {
  padding: 0;
  list-style: none;
  font: 0.74rem/1.45 var(--mono);
}

.file-list li {
  padding: 0.35rem 0;
  border-bottom: 1px solid var(--rule);
  overflow-wrap: anywhere;
}

.chapter-examples {
  margin: 2.5rem 0 -2rem;
  font: 600 0.76rem/1.4 var(--sans);
  letter-spacing: 0.04em;
}

.book-footer {
  position: relative;
  width: 32rem;
  margin: 4rem 0 3rem;
  padding-top: 2.5rem;
  color: var(--nav-text);
  border-top: 1px solid var(--rule);
  font: 0.72rem/1.4 var(--sans);
  text-align: center;
}

.contents-page .book-footer {
  width: 46rem;
}

.book-footer .next {
  position: absolute;
  top: -0.75rem;
  right: 0;
  padding-left: 0.4rem;
  background: white;
  font-size: 0.76rem;
  font-weight: 550;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.typeface-tools {
  width: 100%;
  margin: 4rem 0 0;
  padding-top: 1rem;
  color: var(--muted);
  border-top: 1px solid var(--rule);
  font: 600 0.65rem/1.35 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.typeface-tools label {
  display: flex;
  gap: 0.8rem;
  align-items: center;
  justify-content: flex-end;
}

.typeface-tools span {
  margin: 0;
}

.typeface-tools select {
  width: auto;
  max-width: 100%;
  min-height: 2.1rem;
  padding: 0.25rem 1.8rem 0.25rem 0.55rem;
  color: var(--ink);
  background: var(--code-bg);
  border: 1px solid var(--rule);
  border-radius: 2px;
  font: 400 0.75rem/1.3 var(--sans);
  letter-spacing: 0;
  text-transform: none;
}

.typeface-tools select:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

@media (max-width: 84rem) {
  .book-nav {
    display: none;
  }

  .book-nav-mobile {
    display: flex;
  }

  .page {
    width: min(50.7rem, calc(100% - 3rem));
    margin: 0 auto;
  }

  .typeface-tools {
    width: 100%;
    margin: 4rem 0 0;
  }

  .typeface-tools label {
    display: flex;
    gap: 0.8rem;
    align-items: center;
    justify-content: flex-end;
  }

  .typeface-tools span {
    margin: 0;
  }

  .typeface-tools select {
    width: auto;
    color: var(--ink);
    background: var(--code-bg);
    border-color: var(--rule);
  }
}

@media (max-width: 57rem) {
  .page,
  .contents-page,
  .chapter,
  .book-footer,
  .contents-page .book-footer {
    width: min(32rem, calc(100vw - 3rem));
  }

  .contents-group {
    grid-template-columns: 1fr;
    gap: 2rem;
  }

  .chapter-number {
    top: 2.9rem;
    left: auto;
    right: 0;
    font-size: 4.3rem;
  }

  .margin-note,
  .source-file {
    position: static;
    width: auto;
  }

  .margin-note {
    margin: 1.2rem 0;
    padding: 0.45rem 0;
    border-bottom: 1px solid var(--rule);
  }

  .source-file {
    display: block;
    margin: 0 0 0.35rem;
    text-align: right;
  }

  .source-file::before {
    content: "↓";
  }

  .stack-model,
  .stack-model figcaption,
  .chapter-figure,
  .chapter-figure figcaption {
    width: 100%;
  }

  .chapter table {
    display: block;
    overflow-x: auto;
    white-space: nowrap;
  }
}

@media (max-width: 36rem) {
  :root {
    font-size: 16px;
    line-height: 1.5;
  }

  .page,
  .contents-page,
  .chapter,
  .book-footer,
  .contents-page .book-footer {
    width: calc(100vw - 2rem);
  }

  .book-nav-mobile {
    padding-inline: 0.8rem;
  }

  .chapter-header,
  .contents-header {
    padding-top: 4.8rem;
  }

  .chapter-header h1,
  .contents-header h1 {
    font-size: 2.35rem;
  }

  .chapter-number {
    top: 2.5rem;
    font-size: 3.8rem;
  }

  .chapter h2 {
    margin-top: 3.2rem;
    font-size: 1.45rem;
  }

  .chapter h2 a::before,
  .chapter h3 a::before {
    left: -1rem;
    width: 0.8rem;
  }

  .chapter-note,
  .design-note,
  .code-block {
    margin-inline: 0;
  }

  .chapter table {
    font-size: 0.72rem;
  }

  blockquote p {
    margin-inline: 1.4rem !important;
    font-size: 1.1rem;
  }

  .book-footer .next {
    font-size: 0.68rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  * {
    transition-duration: 0.01ms !important;
  }
}

@media print {
  :root {
    font-size: 11pt;
  }

  @page {
    margin: 18mm;
  }

  .book-nav,
  .book-nav-mobile,
  .skip-link,
  .typeface-tools,
  .source-file,
  .book-footer .next,
  .prototype-note {
    display: none !important;
  }

  .page,
  .chapter,
  .contents-page,
  .book-footer,
  .contents-page .book-footer {
    width: 100%;
    margin: 0;
  }

  .chapter-number {
    right: 0;
    left: auto;
  }

  .margin-note {
    position: static;
    width: auto;
    margin: 1rem 0;
    padding: 0.4rem 0;
    border-bottom: 1px solid #bbb;
  }

  .stack-model,
  .stack-model figcaption,
  .chapter-figure,
  .chapter-figure figcaption {
    width: 100%;
  }

  .code-block,
  .chapter-note,
  .design-note,
  figure {
    break-inside: avoid;
  }

  h2,
  h3 {
    break-after: avoid;
  }

  a {
    color: #000;
  }
}