/* The Learn pages: a chapter list, one chapter of prose and runnable code, and a pager.
 *
 * Long-form reading, so the motion stays out of the way: no reveals on prose, only the
 * copy confirmation, the link underlines and the hover light of the chapter cards (all in
 * motion.css and cards.css). The chapter list is a sticky column on wide screens and a set
 * of wrapping chips above the chapter on narrow ones, so nothing scrolls sideways. */

.learn-wrap {
  display: grid;
  gap: var(--space-xl);
  max-inline-size: var(--page-max);
  margin-inline: auto;
  padding: var(--space-lg) var(--page-gutter) var(--space-3xl);
}

@media (min-width: 64rem) {
  .learn-wrap {
    grid-template-columns: 15rem minmax(0, 1fr);
    gap: var(--space-2xl);
  }
}

/* Chapters on a narrow screen: wrapping chips of links above the chapter, which opens with its
 * own list of sections (.toc). */

.chapters {
  display: grid;
  align-content: start;
  gap: var(--space-sm);
}

.chapters__title {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-muted);
}

.chapters__title a {
  color: inherit;
  text-decoration: none;
}

.chapters ol {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  counter-reset: chapter;
}

.chapters li {
  counter-increment: chapter;
}

.chapters li a {
  display: inline-flex;
  align-items: baseline;
  gap: var(--space-xs);
  padding: var(--space-2xs) var(--space-sm);
  border: var(--rule-hair) solid var(--color-rule-2);
  color: var(--color-ink-2);
  font-size: var(--text-sm);
  text-decoration: none;
  white-space: nowrap;
}

.chapters li a::before {
  content: counter(chapter, decimal-leading-zero);
  font-family: var(--font-mono);
  font-size: var(--text-micro);
  color: var(--color-muted);
}

.chapters li a[aria-current="page"] {
  border-color: var(--color-accent);
  background: var(--color-card-lit);
  color: var(--color-ink);
}

.chapters li a[aria-current="page"]::before {
  color: var(--color-accent);
}

@media (hover: hover) and (pointer: fine) {
  .chapters li a:hover {
    border-color: var(--color-accent);
    color: var(--color-ink);
  }
}

/* The sidebar on a wide screen: the chapters under the parts of the path, every chapter closed to
 * its title (native details, one open at a time through their shared name), the current page's
 * chapter open on its numbered sections.
 * It follows the viewport (sticky, with its own scroll when taller than the window). The script
 * animates the opening and closing and marks the section being read with an indicator that
 * slides to it; without the script it opens and closes all the same. */

.sidebar {
  display: none;
}

.sidebar__num {
  flex: none;
  font-family: var(--font-mono);
  font-size: var(--text-micro);
  color: var(--color-muted);
}

/* An entry is one line: a long section title ends in an ellipsis (its title attribute holds
 * all of it). */
.sidebar__text {
  min-width: 0;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
}

@media (min-width: 64rem) {
  .chapters {
    display: none;
  }

  .sidebar {
    position: sticky;
    inset-block-start: var(--space-lg);
    align-self: start;
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    align-content: start;
    max-block-size: calc(100dvh - 2 * var(--space-lg));
    overflow-y: auto;
    overscroll-behavior: contain;
  }

  .sidebar .chapters__title {
    padding-block-end: var(--space-sm);
  }

  .sidebar__part {
    padding-block: var(--space-md) var(--space-2xs);
    font-family: var(--font-mono);
    font-size: var(--text-micro);
    color: var(--color-muted);
  }

  .sidebar .chapters__title + .sidebar__part {
    padding-block-start: 0;
  }

  .sidebar details {
    border-inline-start: 2px solid var(--color-rule);
  }

  .sidebar details.is-current {
    border-image: var(--fill-liquid) 1;
  }

  .sidebar summary {
    display: flex;
    align-items: baseline;
    white-space: nowrap;
    gap: var(--space-xs);
    padding: var(--space-xs) var(--space-sm);
    color: var(--color-ink-2);
    font-size: var(--text-sm);
    list-style: none;
    cursor: pointer;
  }

  .sidebar summary::-webkit-details-marker {
    display: none;
  }

  /* A chevron at the end of the title: right when closed, down when open. */
  .sidebar summary::after {
    content: "";
    align-self: center;
    margin-inline-start: auto;
    inline-size: 0.45rem;
    block-size: 0.45rem;
    border-block-start: 1.5px solid currentColor;
    border-inline-end: 1.5px solid currentColor;
    color: var(--color-muted);
    transform: translateX(-2px) rotate(45deg);
    transition: transform var(--dur-short) var(--ease-out);
  }

  .sidebar details[open] > summary::after {
    transform: translateY(-2px) rotate(135deg);
  }

  .sidebar details.is-current > summary {
    background: var(--color-card-lit);
    color: var(--color-ink);
  }

  .sidebar details.is-current > summary .sidebar__num {
    color: var(--color-accent);
  }

  .sidebar summary:focus-visible {
    outline-offset: -2px;
  }

  .sidebar ol {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    padding-block-end: var(--space-xs);
  }

  .sidebar ol a {
    min-width: 0;
    display: flex;
    align-items: baseline;
    gap: var(--space-xs);
    padding: var(--space-3xs) var(--space-sm) var(--space-3xs) var(--space-lg);
    color: var(--color-muted);
    font-size: var(--text-xs);
    line-height: 1.4;
    text-decoration: none;
  }

  .sidebar details.is-current ol a {
    color: var(--color-ink-2);
  }

  @media (hover: hover) and (pointer: fine) {
    .sidebar summary:hover,
    .sidebar ol a:hover {
      color: var(--color-ink);
    }

    .sidebar summary:hover::after,
    .sidebar ol a:hover .sidebar__num {
      color: var(--color-accent);
    }
  }

  /* The indicator on the rule beside the section being read. */
  .sidebar__spy {
    position: absolute;
    z-index: 1;
    inset-block-start: 0;
    inset-inline-start: 0;
    inline-size: 2px;
    block-size: 1px;
    background: var(--fill-liquid);
    box-shadow: 0 0 10px 0 var(--color-glow);
    opacity: 0;
    pointer-events: none;
    transform-origin: top;
    transition:
      transform 320ms var(--ease-out),
      opacity var(--dur-short) var(--ease-out);
  }

  .sidebar__spy.is-on {
    opacity: 1;
  }
}

/* The section being read: brighter, its number in the accent. */
.sidebar ol a[aria-current="location"],
.toc a[aria-current="location"] {
  color: var(--color-ink);
}

.sidebar ol a[aria-current="location"] .sidebar__num,
.toc a[aria-current="location"] .sidebar__num {
  color: var(--color-accent);
}

.toc {
  display: grid;
  gap: var(--space-xs);
  padding-block: var(--space-lg) var(--space-xs);
}

.toc__title {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-muted);
}

.toc ol {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-2xs);
}

.toc a {
  min-width: 0;
  display: flex;
  align-items: baseline;
  gap: var(--space-sm);
  color: var(--color-ink-2);
  font-size: var(--text-sm);
  text-decoration: none;
}

@media (min-width: 64rem) {
  .toc {
    display: none;
  }
}

/* A chapter. */

.learn-main {
  min-width: 0;
  max-inline-size: 52rem;
}

.chapter-head {
  display: grid;
  gap: var(--space-md);
  padding-block-end: var(--space-xl);
  border-block-end: var(--rule-hair) solid var(--color-rule);
}

.chapter-head__step {
  justify-self: start;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
}

.chapter-head h1 {
  font-size: clamp(2.5rem, 3.5vw + 1rem, 4rem);
  line-height: 1.02;
  letter-spacing: var(--tracking-display);
  text-wrap: balance;
}

.chapter-head__lede {
  max-inline-size: 60ch;
  font-size: var(--text-md);
  color: var(--color-ink-2);
}

.prose {
  display: grid;
  gap: var(--space-md);
  padding-block-start: var(--space-lg);
}

.prose > * {
  min-width: 0;
}

.prose h2 {
  margin-block-start: var(--space-2xl);
  font-size: var(--text-2xl);
  line-height: 1.12;
  letter-spacing: var(--tracking-head);
  scroll-margin-block-start: var(--space-lg);
}

.prose > h2:first-child {
  margin-block-start: var(--space-md);
}

.prose h3 {
  margin-block-start: var(--space-lg);
  font-size: var(--text-lg);
  scroll-margin-block-start: var(--space-lg);
}

.prose p,
.prose li {
  max-inline-size: 68ch;
}

.prose strong {
  font-weight: 600;
  color: var(--color-ink);
}

.prose :not(pre) > code {
  padding: 0.05em 0.3em;
  border: var(--rule-hair) solid var(--color-rule);
  background: var(--color-paper-2);
  overflow-wrap: anywhere;
}

.prose ul,
.prose ol {
  display: grid;
  gap: var(--space-xs);
}

.prose ul li,
.prose ol li {
  position: relative;
  padding-inline-start: var(--space-lg);
}

.prose ul li::before {
  content: "";
  position: absolute;
  inset-block-start: 0.62em;
  inset-inline-start: 0.2rem;
  inline-size: 0.35rem;
  block-size: 0.35rem;
  background: var(--fill-liquid);
}

.prose ol {
  counter-reset: item;
}

.prose ol li {
  counter-increment: item;
}

.prose ol li::before {
  content: counter(item);
  position: absolute;
  inset-inline-start: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  line-height: 1.9;
  color: var(--color-accent);
}

/* A code sample with what it is above it: a file name, or what to type. */
.snippet {
  display: grid;
  gap: var(--space-xs);
  margin-block: var(--space-xs);
}

.snippet__label {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-muted);
}

.snippet .code pre {
  font-size: var(--text-xs);
}

@media (min-width: 40rem) {
  .snippet .code pre {
    font-size: var(--text-sm);
  }
}

/* Output a program prints: plain, set back from the code. */
.snippet--output .code {
  background: var(--color-paper);
  box-shadow: none;
}

.snippet--output .code pre {
  color: var(--color-muted);
}

/* A note: a fact worth stopping for, behind a bar of the liquid. */
.note {
  position: relative;
  display: grid;
  gap: var(--space-2xs);
  padding: var(--space-md) var(--space-lg);
  background: linear-gradient(90deg, var(--color-card-emit) 0%, transparent 80%);
}

.note::before {
  content: "";
  position: absolute;
  inset-block: 0;
  inset-inline-start: 0;
  inline-size: 2px;
  background: var(--fill-liquid);
}

.note__title {
  font-weight: 600;
  color: var(--color-ink);
}

/* Tables: rows of facts. On a phone each row becomes a block, its cells labelled. */
.table {
  inline-size: 100%;
  border-collapse: collapse;
  font-size: var(--text-sm);
}

.table th {
  padding: var(--space-xs) var(--space-sm);
  border-block-end: var(--rule-hair) solid var(--color-rule-2);
  color: var(--color-muted);
  font-weight: 500;
  text-align: start;
}

.table td {
  padding: var(--space-sm);
  border-block-end: var(--rule-hair) solid var(--color-rule);
  vertical-align: top;
}

.table th:first-child,
.table td:first-child {
  padding-inline-start: 0;
}

/* A name in the first column stays whole; the row wraps between names instead. */
.table td:first-child code {
  white-space: nowrap;
}

@media (max-width: 39.99rem) {
  .table thead {
    position: absolute;
    inline-size: 1px;
    block-size: 1px;
    overflow: hidden;
    clip-path: inset(50%);
  }

  /* Blocks, not a table: the column the widest cell sets would run off the screen. */
  .table,
  .table tbody {
    display: block;
  }

  .table tr {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-2xs);
    padding-block: var(--space-sm);
    border-block-end: var(--rule-hair) solid var(--color-rule);
  }

  /* A cell is a block, so its text and inline code flow as one paragraph under its label. */
  .table td {
    display: block;
    min-width: 0;
    padding: 0;
    border: 0;
  }

  .table td::before {
    content: attr(data-label);
    display: block;
    margin-block-end: var(--space-3xs);
    font-family: var(--font-mono);
    font-size: var(--text-micro);
    color: var(--color-muted);
  }

  .table td:first-child code {
    white-space: normal;
  }
}

/* Previous and next. */
.pager {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-sm);
  margin-block-start: var(--space-3xl);
}

/* Each link one line: a drawn chevron and the chapter's name. */
.pager a {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  min-width: 0;
  padding: var(--space-md);
  border: var(--rule-hair) solid var(--color-rule-2);
  background: var(--color-paper-2);
  text-decoration: none;
}

.pager a[rel="next"] {
  grid-column: 2;
  justify-content: flex-end;
}

.pager a[rel="prev"]::before,
.pager a[rel="next"]::after {
  content: "";
  flex: none;
  inline-size: 0.5rem;
  block-size: 0.5rem;
  border-block-start: 1.5px solid var(--color-accent);
  border-inline-end: 1.5px solid var(--color-accent);
}

.pager a[rel="prev"]::before {
  rotate: -135deg;
}

.pager a[rel="next"]::after {
  rotate: 45deg;
}

.pager__title {
  overflow: hidden;
  color: var(--color-ink);
  font-weight: 600;
  white-space: nowrap;
  text-overflow: ellipsis;
}

@media (hover: hover) and (pointer: fine) {
  .pager a:hover {
    border-color: var(--color-accent);
  }
}

/* The Learn index: the parts of the path, each a heading over a card per chapter. */
.learn-part {
  padding-block-start: var(--space-2xl);
}

.learn-part h2 {
  font-size: var(--text-xl);
  line-height: 1.12;
  letter-spacing: var(--tracking-head);
}

.learn-cards {
  display: grid;
  gap: var(--space-md);
  padding-block-start: var(--space-lg);
}

@media (min-width: 40rem) {
  .learn-cards {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (min-width: 72rem) {
  .learn-cards {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
}

a.card {
  grid-column: auto;
  color: var(--color-ink-2);
  text-decoration: none;
}

.card__step {
  justify-self: start;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
}

.card p:last-child {
  font-size: var(--text-sm);
}

/* Back to top: a square in the mark's colours at the corner of the screen. Without the script it
 * is always there; site.js rests it while the bar at the top of the page is in view. */

.to-top {
  position: fixed;
  inset-block-end: var(--space-lg);
  inset-inline-end: var(--page-gutter);
  z-index: var(--z-raised);
  display: grid;
  place-items: center;
  inline-size: 2.75rem;
  block-size: 2.75rem;
  background: var(--fill-square);
  box-shadow: inset 0 1px 0 var(--color-gloss-strong), 0 12px 32px -12px var(--color-glow);
  color: var(--color-paper);
}

.to-top svg {
  inline-size: 1.25rem;
  block-size: 1.25rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: square;
}

.to-top[data-rest] {
  opacity: 0;
  visibility: hidden;
  transform: translateY(var(--rise));
}

.to-top:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 3px;
}

/* The pager and the footer's links keep clear of it at the bottom of the page. */
.learn-wrap ~ .foot {
  padding-block-end: calc(var(--space-lg) + 2.75rem + var(--space-lg));
}

@media print {
  .to-top {
    display: none;
  }
}