/* Page frame: the shell, the header, the label rail beside each section,
   and the footer. */

.shell {
  width: min(100% - var(--gutter) * 2, var(--shell));
  margin-inline: auto;
}

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: var(--paper);
  background: color-mix(in srgb, var(--paper) 82%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid transparent;
  transition: border-color var(--t-mid) var(--ease), background-color var(--t-mid) var(--ease);
}

.site-header.is-stuck { border-bottom-color: var(--line); }

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--s-4);
  height: var(--header);
}

.logo {
  font-family: var(--font-mono);
  font-size: var(--text-base);
  font-weight: 500;
  letter-spacing: -0.03em;
  color: var(--ink);
  background-image: none;
}

.logo:hover { color: var(--ink); }

.logo__x {
  display: inline-block;
  color: var(--blue);
  transition: transform var(--t-mid) var(--ease-out);
}

.logo:hover .logo__x { transform: rotate(-90deg); }

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

/* Nav --------------------------------------------------------------------- */

.nav {
  display: flex;
  align-items: center;
  gap: clamp(0.75rem, 2.5vw, 1.75rem);
}

.nav__link {
  position: relative;
  padding: 0.35rem 0;
  font-size: var(--text-sm);
  color: var(--ink-soft);
  background-image: none;
}

.nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1px;
  background: var(--blue);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--t-mid) var(--ease-out);
}

.nav__link:hover,
.nav__link.is-current { color: var(--blue-deep); }

.nav__link:hover::after,
.nav__link.is-current::after { transform: scaleX(1); }

.progress {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -1px;
  height: 2px;
}

.progress span {
  display: block;
  height: 100%;
  background: var(--blue);
  transform: scaleX(var(--progress, 0));
  transform-origin: left;
}

/* Sections ---------------------------------------------------------------- */

main { position: relative; }

/* The hairline that runs the height of the page beside the rail labels.
   Only drawn when the shell is at full width and the rail has its own column. */
@media (min-width: 73rem) {
  main {
    background-image: linear-gradient(var(--line-soft), var(--line-soft));
    background-repeat: no-repeat;
    background-size: 1px 100%;
    background-position: calc(50% - var(--shell) / 2 + var(--rail)) 0;
  }
}

.band { padding: var(--s-7) 0; }

.band + .band { border-top: 1px solid var(--line); }

.band__inner {
  display: grid;
  grid-template-columns: var(--rail) minmax(0, 1fr);
}

.band__body { min-width: 0; }

.rail {
  position: sticky;
  top: calc(var(--header) + var(--s-4));
  align-self: start;
  padding-top: 0.45rem;
}

@media (min-width: 73rem) {
  .band__body { padding-left: var(--s-4); }
}

@media (max-width: 60rem) {
  .band__inner { grid-template-columns: minmax(0, 1fr); }

  .rail {
    position: static;
    padding-top: 0;
    margin-bottom: var(--s-3);
  }
}

/* The rail label of the section currently in view darkens. */
.band.is-active .rail { color: var(--blue-deep); }

.band--hero { padding-top: clamp(4rem, 11vw, 7rem); }

.band--hero .rail { color: var(--ink-faint); }

/* Footer ------------------------------------------------------------------ */

.site-footer {
  border-top: 1px solid var(--line);
  padding: var(--s-5) 0 var(--s-6);
  color: var(--ink-soft);
  font-size: var(--text-sm);
}

.site-footer__inner {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--s-3) var(--s-4);
}

.site-footer p { margin: 0; }

.to-top {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: var(--tracking-label);
  text-transform: uppercase;
}