/* ============================================================
   layout.css — masthead, shell grid, reading scale, chapters
   ============================================================ */

/* ── masthead ─────────────────────────────────────────────── */
.masthead {
  position: fixed;
  inset: 0 0 auto;
  z-index: 50;
  height: var(--masthead-h);
  display: flex;
  align-items: center;
  gap: var(--space-m);
  padding-inline: var(--gutter);
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(14px) saturate(1.4);
  -webkit-backdrop-filter: blur(14px) saturate(1.4);
  border-bottom: var(--hair) solid transparent;
  transition: border-color var(--dur-mid) var(--ease-out),
              background-color var(--dur-mid) var(--ease-out);
}

.masthead[data-stuck='true'] { border-bottom-color: var(--rule); }

.masthead__mark {
  display: flex;
  align-items: center;
  gap: var(--space-2xs);
  flex: none;
}

.masthead__initials {
  font-family: var(--font-display);
  font-weight: 800;
  font-variation-settings: 'wdth' 120;
  font-size: var(--step-0);
  letter-spacing: 0.01em;
}

.masthead__rule {
  width: 1.5rem;
  height: var(--hair);
  background: var(--signal);
  transition: width var(--dur-mid) var(--ease-out);
}

.masthead__mark:hover .masthead__rule { width: 2.5rem; }

.menu-toggle { display: none; }

.masthead__nav { margin-inline-start: auto; }

.masthead__nav ul {
  display: flex;
  gap: clamp(var(--space-s), 2vw, var(--space-l));
}

.masthead__nav a {
  font-family: var(--font-mono);
  font-size: var(--step--2);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-soft);
  padding-block: var(--space-2xs);
  position: relative;
  transition: color var(--dur-fast) var(--ease-out);
}

.masthead__nav a::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: 0;
  width: 100%;
  height: var(--hair);
  background: currentColor;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--dur-mid) var(--ease-out);
}

.masthead__nav a:hover,
.masthead__nav a[aria-current='true'] { color: var(--ink); }
.masthead__nav a:hover::after,
.masthead__nav a[aria-current='true']::after { transform: scaleX(1); }
.masthead__nav a[aria-current='true'] { color: var(--signal); }

/* Slim progress rail — the mobile stand-in for the scale */
.masthead__progress {
  position: absolute;
  inset: auto 0 0;
  height: 2px;
  background: transparent;
  pointer-events: none;
}

.masthead__progress span {
  display: block;
  height: 100%;
  width: 100%;
  background: var(--live);
  transform: scaleX(0);
  transform-origin: left;
}

@media (min-width: 68.75rem) {
  .masthead__progress { display: none; }
}

/* ── theme toggle ─────────────────────────────────────────── */
.theme-toggle {
  flex: none;
  display: flex;
  align-items: center;
  gap: var(--space-2xs);
  padding: var(--space-3xs) var(--space-2xs) var(--space-3xs) var(--space-3xs);
  border: var(--hair) solid var(--rule);
  font-family: var(--font-mono);
  font-size: var(--step--2);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-soft);
  transition: border-color var(--dur-fast) var(--ease-out),
              color var(--dur-fast) var(--ease-out);
}

.theme-toggle:hover { border-color: var(--ink-faint); color: var(--ink); }

.theme-toggle__icon {
  flex: none;
  display: grid;
  width: 1rem;
  height: 1rem;
  place-items: center;
  color: var(--signal);
  transition: color var(--dur-fast) var(--ease-out);
}

.theme-toggle__icon svg {
  grid-area: 1 / 1;
  width: 100%;
  height: 100%;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
  transition: opacity var(--dur-fast) var(--ease-out),
              transform var(--dur-fast) var(--ease-out);
}

.theme-toggle__moon { opacity: 1; }

.theme-toggle__sun {
  opacity: 0;
  transform: rotate(-25deg) scale(0.75);
}

[data-theme='dark'] .theme-toggle__icon { color: var(--live); }

[data-theme='dark'] .theme-toggle__moon {
  opacity: 0;
  transform: rotate(25deg) scale(0.75);
}

[data-theme='dark'] .theme-toggle__sun {
  opacity: 1;
  transform: none;
}

@media (max-width: 46.875rem) {
  .masthead { gap: var(--space-xs); }

  .menu-toggle:not([hidden]) {
    min-width: 4.5rem;
    min-height: 2.75rem;
    margin-inline-start: auto;
    padding-inline: var(--space-xs);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-2xs);
    border: var(--hair) solid var(--rule);
    color: var(--ink-soft);
    font-family: var(--font-mono);
    font-size: var(--step--2);
    letter-spacing: 0.1em;
    text-transform: uppercase;
    touch-action: manipulation;
    transition: border-color var(--dur-fast) var(--ease-out),
                color var(--dur-fast) var(--ease-out);
  }

  .menu-toggle:hover,
  .menu-toggle[aria-expanded='true'] {
    border-color: var(--ink-faint);
    color: var(--ink);
  }

  .menu-toggle__icon {
    width: 0.9rem;
    display: grid;
    gap: 0.25rem;
  }

  .menu-toggle__icon span {
    display: block;
    width: 100%;
    height: var(--hair);
    background: currentColor;
    transition: transform var(--dur-fast) var(--ease-out);
  }

  .menu-toggle[aria-expanded='true'] .menu-toggle__icon span:first-child {
    transform: translateY(0.15rem) rotate(45deg);
  }

  .menu-toggle[aria-expanded='true'] .menu-toggle__icon span:last-child {
    transform: translateY(-0.15rem) rotate(-45deg);
  }

  .masthead__nav {
    position: absolute;
    inset: 100% 0 auto;
    margin: 0;
    padding: var(--space-xs) var(--gutter) var(--space-s);
    background: color-mix(in srgb, var(--bg) 96%, transparent);
    backdrop-filter: blur(14px) saturate(1.4);
    -webkit-backdrop-filter: blur(14px) saturate(1.4);
    border-bottom: var(--hair) solid var(--rule);
  }

  .masthead__nav[data-menu-enhanced='true'] {
    visibility: hidden;
    opacity: 0;
    pointer-events: none;
    transform: translateY(-0.5rem);
    transition: visibility 0s linear var(--dur-fast),
                opacity var(--dur-fast) var(--ease-out),
                transform var(--dur-fast) var(--ease-out);
  }

  .masthead__nav[data-menu-enhanced='true'][data-open='true'] {
    visibility: visible;
    opacity: 1;
    pointer-events: auto;
    transform: translateY(0);
    transition-delay: 0s;
  }

  .masthead__nav ul {
    display: grid;
    gap: 0;
  }

  .masthead__nav li + li { border-top: var(--hair) solid var(--rule-soft); }

  .masthead__nav a {
    min-height: 2.75rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding-block: var(--space-xs);
    touch-action: manipulation;
  }

  .masthead__nav a::after {
    display: none;
  }

  .theme-toggle {
    min-width: 2.75rem;
    min-height: 2.75rem;
    justify-content: center;
    padding: 0;
    touch-action: manipulation;
  }

  .theme-toggle__label { display: none; }
}

@media (max-width: 22rem) {
  .menu-toggle { min-width: 2.75rem; padding: 0; }
  .menu-toggle__label { display: none; }
}

@media (prefers-reduced-motion: reduce) {
  .theme-toggle__icon,
  .theme-toggle__icon svg,
  .menu-toggle__icon span,
  .masthead__nav[data-menu-enhanced='true'] { transition: none; }
}

/* ── shell: scale + flow ──────────────────────────────────── */
.shell {
  display: grid;
  grid-template-columns: minmax(0, var(--col-scale)) minmax(0, var(--col-flow));
  gap: var(--shell-gap);
  justify-content: center;
  padding-inline: var(--gutter);
  padding-bottom: var(--space-3xl);
}

.flow { min-width: 0; }

@media (max-width: 68.6875rem) {
  .shell { grid-template-columns: minmax(0, var(--col-flow)); }
  .scale { display: none; }
}

/* ── the reading scale (signature element) ────────────────── */
.scale {
  position: sticky;
  top: calc(var(--masthead-h) + var(--space-xl));
  align-self: start;
  height: fit-content;
  user-select: none;
}

.scale__title,
.scale__foot { color: var(--ink-faint); }

.scale__title { margin-bottom: var(--space-m); }

.scale__body {
  position: relative;
  height: min(58vh, 26rem);
  min-height: 18rem;
}

/* the axis line */
.scale__axis {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 5.5rem;
  width: var(--hair);
  background: var(--rule);
}

/* minor graduations, every 10px */
.scale__ticks {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 4.55rem;
  width: 0.6rem;
  background-image: repeating-linear-gradient(
    to bottom,
    var(--rule) 0 var(--hair),
    transparent var(--hair) 10px
  );
  opacity: 0.75;
}

/* named graduations — JS calibrates `top` to real chapter offsets */
.scale__marks { position: absolute; inset: 0; }

.scale__mark {
  position: absolute;
  left: 0;
  right: 0;
  top: var(--pos, 0%);
  transform: translateY(-50%);
}

.scale__mark a {
  display: grid;
  grid-template-columns: 1.75rem 1fr;
  align-items: center;
  gap: 0.45rem;
  padding-left: 6.25rem;
  height: 1.6rem;
  font-family: var(--font-mono);
  font-size: var(--step--2);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-faint);
  transition: color var(--dur-mid) var(--ease-out);
}

/* major tick, drawn leftward from the axis */
.scale__mark a::before {
  content: '';
  position: absolute;
  left: 3.9rem;
  top: 50%;
  width: 1.65rem;
  height: var(--hair);
  background: var(--rule);
  transform: translateY(-50%);
  transition: background-color var(--dur-mid) var(--ease-out),
              width var(--dur-mid) var(--ease-out),
              left var(--dur-mid) var(--ease-out);
}

.scale__num { color: var(--ink-faint); transition: color var(--dur-mid) var(--ease-out); }
.scale__name { transition: color var(--dur-mid) var(--ease-out); }

.scale__mark a:hover { color: var(--ink); }
.scale__mark a:hover::before { background: var(--ink-faint); }

/* passed */
.scale__mark[data-state='past'] a { color: var(--ink-soft); }
.scale__mark[data-state='past'] a::before { background: var(--ink-faint); }

/* current */
.scale__mark[data-state='current'] a { color: var(--ink); }
.scale__mark[data-state='current'] .scale__num { color: var(--signal); }
.scale__mark[data-state='current'] a::before {
  background: var(--signal);
  left: 3.4rem;
  width: 2.15rem;
}

/* the live indicator */
.scale__indicator {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  height: 0;
  will-change: transform;
  z-index: 2;
}

.scale__indicator-arrow {
  position: absolute;
  left: 4.9rem;
  top: 0;
  width: 1.2rem;
  height: var(--hair);
  background: var(--live);
  transform: translateY(-50%);
}

.scale__indicator-arrow::after {
  content: '';
  position: absolute;
  right: -1px;
  top: 50%;
  width: 0.4rem;
  height: 0.4rem;
  background: var(--live);
  transform: translate(0, -50%) rotate(45deg);
}

.scale__indicator-readout {
  position: absolute;
  /* stops short of the active graduation tick at 3.4rem */
  right: calc(100% - 3rem);
  top: 0;
  transform: translateY(-50%);
  font-family: var(--font-mono);
  font-size: var(--step--2);
  font-weight: 500;
  letter-spacing: 0.06em;
  color: var(--live);
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.scale__foot {
  margin-top: var(--space-m);
  padding-top: var(--space-s);
  border-top: var(--hair) solid var(--rule-soft);
  font-size: var(--step--2);
}

/* ── chapters ─────────────────────────────────────────────── */
.chapter { padding-top: var(--space-3xl); }
.chapter:first-child { padding-top: var(--space-2xl); }

.chapter__head { margin-bottom: var(--space-l); }

.chapter__index {
  color: var(--ink-faint);
  margin-bottom: var(--space-s);
}

.chapter__title {
  font-size: var(--step-4);
  max-width: 20ch;
}

/* ── colophon ─────────────────────────────────────────────── */
.colophon {
  border-top: var(--hair) solid var(--rule);
  padding: var(--space-l) var(--gutter);
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-s) var(--space-l);
}

.colophon__name {
  font-family: var(--font-display);
  font-weight: 700;
  font-variation-settings: 'wdth' 112;
}

.colophon__meta { color: var(--ink-faint); }

.colophon__top {
  margin-inline-start: auto;
  font-family: var(--font-mono);
  font-size: var(--step--2);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-soft);
  transition: color var(--dur-fast) var(--ease-out);
}

.colophon__top:hover { color: var(--signal); }