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

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-padding-top: var(--header-h);
  background: var(--night);
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: 400;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  overflow-x: clip;
}

img,
video,
canvas {
  display: block;
  max-width: 100%;
}

h1,
h2,
h3,
p,
ol,
ul,
figure {
  margin: 0;
}

ol,
ul {
  padding: 0;
  list-style: none;
}

a {
  color: inherit;
  text-decoration-thickness: 1px;
  text-underline-offset: 0.22em;
}

button,
input,
select {
  font: inherit;
  color: inherit;
}

:focus-visible {
  outline: 2px solid var(--scene-accent);
  outline-offset: 3px;
  border-radius: 2px;
}

.visually-hidden {
  position: absolute !important;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 100;
  padding: 0.55rem 0.9rem;
  border-radius: var(--radius-s);
  background: var(--sheet);
  color: var(--ink);
  font-weight: 500;
  text-decoration: none;
  transform: translateY(-160%);
  transition: transform var(--duration-normal) var(--ease-out);
}

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

/* ---------- Headings shared by every surface ---------- */

.title {
  font-family: var(--font-display);
  font-size: var(--text-h2);
  font-weight: 500;
  font-optical-sizing: auto;
  line-height: 1.06;
  letter-spacing: -0.018em;
  text-wrap: balance;
}

/* Handwritten note: the one human mark, used sparingly */
.note {
  font-family: var(--font-hand);
  font-size: var(--text-note);
  line-height: 1.2;
  color: var(--scene-accent);
  transform: rotate(-2.5deg);
  transform-origin: left center;
}

/* ---------- Header ---------- */

.site-header {
  position: fixed;
  inset: 0 0 auto;
  z-index: 50;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  height: var(--header-h);
  padding: 0 var(--gutter);
  color: var(--scene-fg);
  transition: color var(--duration-slow) var(--ease-soft);
}

.site-header::before {
  content: '';
  position: absolute;
  inset: 0 0 -1.5rem;
  z-index: -1;
  background: linear-gradient(to bottom, color-mix(in srgb, var(--header-bg, var(--scene)) 90%, transparent) 55%, transparent);
  pointer-events: none;
}

.wordmark {
  justify-self: start;
  font-family: var(--font-display);
  font-size: 1.3rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  text-decoration: none;
}

.chapter-label {
  color: var(--scene-fg-soft);
  font-size: var(--text-sm);
  font-variant-numeric: tabular-nums;
  transition: opacity var(--duration-normal);
}

.chapter-label[data-hidden='true'] {
  opacity: 0;
}

.header-link {
  justify-self: end;
  font-size: var(--text-sm);
  font-weight: 500;
  text-decoration-color: color-mix(in srgb, currentColor 40%, transparent);
  transition: color var(--duration-fast), text-decoration-color var(--duration-fast);
}

.header-link:hover {
  color: var(--scene-accent);
  text-decoration-color: currentColor;
}

.progress {
  position: fixed;
  inset: 0 0 auto;
  z-index: 60;
  height: 2px;
  background: var(--scene-accent);
  transform: scaleX(0);
  transform-origin: 0 50%;
  pointer-events: none;
}

@media (max-width: 640px) {
  .site-header {
    grid-template-columns: auto 1fr auto;
    gap: 0.75rem;
  }

  .chapter-label {
    justify-self: center;
    font-size: var(--text-xs);
  }
}

/* ---------- Buttons and links ---------- */

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 3.25rem;
  padding: 0.85rem 1.5rem;
  border: 0;
  border-radius: var(--radius-s);
  background: var(--ink);
  color: var(--sheet);
  font-weight: 500;
  cursor: pointer;
  transition:
    background-color var(--duration-fast),
    transform var(--duration-fast) var(--ease-out);
}

.button:hover {
  background: var(--ribbon);
}

.button:active {
  transform: translateY(1px);
}

.button[aria-busy='true'] {
  cursor: progress;
  opacity: 0.75;
}

.text-link {
  color: var(--ribbon);
  font-weight: 500;
  text-decoration-color: color-mix(in srgb, currentColor 45%, transparent);
  transition: text-decoration-color var(--duration-fast);
}

.text-link:hover {
  text-decoration-color: currentColor;
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 1ms !important;
    animation-duration: 1ms !important;
    animation-iteration-count: 1 !important;
  }
}