/* ============================================================
   Shared site header
   One component for both site versions. academic.css and
   styles.css each map their own palette onto the --hd-* tokens,
   so the header keeps a single structure, layout and behaviour
   while staying in the colour world of the page it sits on.

   Required tokens (see the mapping block in each stylesheet):
   --hd-font, --hd-pad-x, --hd-bg, --hd-panel, --hd-surface,
   --hd-on-solid, --hd-fg, --hd-fg-dim, --hd-line, --hd-line-soft,
   --hd-accent, --hd-t, --hd-t-fast, --hd-ease
   ============================================================ */

/* Opacity-only entrance. */
@keyframes hd-enter {
  from { opacity: 0; }
  to { opacity: 1; }
}

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 200;
  font-family: var(--hd-font);
  animation: hd-enter 0.5s var(--hd-ease) both;
}
.site-header.is-hidden {
  transform: none;
}

.hd-bar {
  display: flex;
  align-items: center;
  gap: clamp(14px, 2.5vw, 26px);
  padding: 13px var(--hd-pad-x);
  background: var(--hd-bg);
  backdrop-filter: blur(14px) saturate(1.25);
  -webkit-backdrop-filter: blur(14px) saturate(1.25);
  border-bottom: 1px solid transparent;
  transition: padding var(--hd-t) var(--hd-ease), border-color var(--hd-t) var(--hd-ease);
}
.site-header.is-stuck .hd-bar {
  padding-block: 9px;
  border-bottom-color: var(--hd-line-soft);
}

/* Reading progress, pinned to the bottom edge of the bar */
.hd-progress { display: none; }

/* ---------- Brand ---------- */
.hd-brand {
  display: inline-flex;
  align-items: baseline;
  gap: 0;
  color: var(--hd-fg);
  white-space: nowrap;
}
.hd-brand-mark { display: none; }
.hd-brand-name {
  font-size: 0.94rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

/* ---------- Links ---------- */
.hd-links {
  display: flex;
  align-items: center;
  gap: clamp(16px, 2vw, 26px);
  margin-left: auto;
}
.hd-links a {
  position: relative;
  padding-block: 4px;
  font-size: 0.88rem;
  color: var(--hd-fg-dim);
  transition: color var(--hd-t-fast) var(--hd-ease);
}
.hd-links a::after {
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1px;
  background: currentColor;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--hd-t) var(--hd-ease);
}
.hd-links a:hover,
.hd-links a:focus-visible { color: var(--hd-fg); }
.hd-links a:hover::after,
.hd-links a:focus-visible::after { transform: scaleX(1); }
/* Current page, or the section currently in view */
.hd-links a[aria-current],
.hd-links a.is-current {
  color: var(--hd-fg);
}
.hd-links a[aria-current]::after,
.hd-links a.is-current::after {
  transform: scaleX(1);
  background: var(--hd-accent);
}

/* ---------- Actions ---------- */
.hd-actions {
  display: flex;
  align-items: center;
  gap: 8px;
  padding-left: clamp(12px, 2vw, 22px);
  border-left: 1px solid var(--hd-line-soft);
}

/* Academic ⇄ Design version switch */
.hd-switch {
  position: relative;
  display: inline-grid;
  grid-template-columns: 1fr 1fr;
  padding: 3px;
  border: 1px solid var(--hd-line-soft);
  border-radius: 999px;
  background: var(--hd-surface);
}
.hd-switch-thumb {
  position: absolute;
  top: 3px;
  bottom: 3px;
  left: 3px;
  width: calc(50% - 3px);
  border-radius: 999px;
  background: var(--hd-fg);
  transform: translateX(0);
  transition: transform 340ms var(--hd-ease);
}
.hd-switch[data-mode="design"] .hd-switch-thumb { transform: translateX(100%); }
/* Hovering the other side previews the move before you commit to it */
.hd-switch:has(.hd-switch-opt + .hd-switch-opt:hover) .hd-switch-thumb { transform: translateX(100%); }
.hd-switch:has(.hd-switch-opt:first-of-type:hover) .hd-switch-thumb { transform: translateX(0); }

.hd-switch-opt {
  position: relative;
  padding: 5px 13px;
  border-radius: 999px;
  font-size: 0.7rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  text-align: center;
  color: var(--hd-fg-dim);
  white-space: nowrap;
  transition: color var(--hd-t-fast) var(--hd-ease);
}
.hd-switch[data-mode="academic"] .hd-switch-opt:first-of-type,
.hd-switch[data-mode="design"] .hd-switch-opt:last-of-type {
  color: var(--hd-on-solid);
}
.hd-switch:has(.hd-switch-opt:hover) .hd-switch-opt { color: var(--hd-fg-dim); }
.hd-switch:has(.hd-switch-opt:hover) .hd-switch-opt:hover { color: var(--hd-on-solid); }

/* Icon buttons */
.hd-icon-btn {
  width: 34px;
  height: 34px;
  flex: none;
  display: inline-grid;
  place-items: center;
  position: relative;
  border: 1px solid var(--hd-line-soft);
  border-radius: 50%;
  color: var(--hd-fg-dim);
  background: transparent;
  transition: color var(--hd-t-fast) var(--hd-ease), border-color var(--hd-t-fast) var(--hd-ease),
    background var(--hd-t-fast) var(--hd-ease);
}
.hd-icon-btn:hover {
  color: var(--hd-fg);
  border-color: var(--hd-line);
  background: var(--hd-surface);
}
.hd-icon-btn svg { width: 16px; height: 16px; }

.hd-theme svg {
  position: absolute;
  transition: transform var(--hd-t) var(--hd-ease), opacity var(--hd-t) var(--hd-ease);
}
[data-theme="light"] .hd-icon-moon { opacity: 0; transform: rotate(-60deg) scale(0.5); }
[data-theme="dark"] .hd-icon-sun { opacity: 0; transform: rotate(60deg) scale(0.5); }

/* Menu button — only shown once the links collapse */
.site-header.is-navless .hd-burger,
.site-header.is-navless .hd-links { display: none !important; }
.hd-burger-box {
  position: relative;
  width: 15px;
  height: 10px;
}
.hd-burger-box span {
  position: absolute;
  left: 0;
  width: 100%;
  height: 1.5px;
  border-radius: 2px;
  background: currentColor;
  transition: transform var(--hd-t) var(--hd-ease), opacity var(--hd-t-fast) var(--hd-ease);
}
.hd-burger-box span:first-child { top: 0; }
.hd-burger-box span:last-child { bottom: 0; }
.site-header.is-open .hd-burger-box span:first-child { transform: translateY(4.25px) rotate(45deg); }
.site-header.is-open .hd-burger-box span:last-child { transform: translateY(-4.25px) rotate(-45deg); }

/* ---------- Skip link ---------- */
.hd-skip {
  position: absolute;
  left: -9999px;
  top: 0;
}
.hd-skip:focus {
  left: 12px;
  top: 12px;
  z-index: 300;
  padding: 10px 16px;
  font-family: var(--hd-font);
  font-size: 0.85rem;
  background: var(--hd-fg);
  color: var(--hd-on-solid);
  border-radius: 8px;
}

.site-header :focus-visible {
  outline: 2px solid var(--hd-accent);
  outline-offset: 3px;
  border-radius: 4px;
}

.email-copy-toast {
  position: fixed;
  left: 50%;
  top: 74px;
  z-index: 360;
  padding: 9px 14px;
  border: 1px solid var(--hd-line-soft);
  border-radius: 999px;
  font-family: var(--hd-font);
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--hd-fg);
  background: var(--hd-panel);
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.12);
  opacity: 0;
  transform: translate(-50%, -8px);
  pointer-events: none;
  transition: opacity var(--hd-t) var(--hd-ease), transform var(--hd-t) var(--hd-ease);
}
.email-copy-toast.is-visible {
  opacity: 1;
  transform: translate(-50%, 0);
}

/* ---------- Shared page transition ---------- */
.page-transition {
  position: fixed;
  inset: 0;
  z-index: 300;
  display: grid;
  place-items: center;
  pointer-events: none;
  background:
    linear-gradient(135deg, color-mix(in srgb, var(--hd-panel) 94%, var(--hd-accent) 6%), var(--hd-panel));
  transform: translateY(100%);
  opacity: 1;
  overflow: hidden;
}
.page-transition::before,
.page-transition::after {
  content: '';
  position: absolute;
  inset: auto -8vw;
  height: 34vh;
  border-radius: 50%;
  background: color-mix(in srgb, var(--hd-accent) 14%, transparent);
  filter: blur(42px);
  transform: translateY(18vh) rotate(-8deg);
}
.page-transition::after {
  top: -22vh;
  bottom: auto;
  opacity: 0.54;
  transform: translateY(0) rotate(8deg);
}
.page-transition.enter {
  animation: hd-page-cover 620ms var(--hd-ease) forwards;
}
.page-transition.exit {
  transform: translateY(0);
  animation: hd-page-reveal 680ms var(--hd-ease) forwards;
}
.page-transition-inner {
  position: relative;
  z-index: 1;
  display: inline-flex;
  align-items: center;
  gap: 12px;
  color: var(--hd-fg);
}
.page-transition-mark,
.page-transition-inner::before {
  content: '';
  width: 30px;
  height: 1px;
  background: var(--hd-accent);
  transform-origin: left;
  animation: hd-load-line 900ms var(--hd-ease) infinite;
}
.page-transition-mark + .page-transition-label,
.page-transition-label {
  font-family: var(--hd-font);
  font-size: 0.74rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--hd-fg-dim);
}
@keyframes hd-page-cover {
  0% { transform: translateY(100%); }
  100% { transform: translateY(0); }
}
@keyframes hd-page-reveal {
  0% { transform: translateY(0); }
  100% { transform: translateY(-100%); }
}
@keyframes hd-load-line {
  0%, 100% { transform: scaleX(0.35); opacity: 0.35; }
  50% { transform: scaleX(1); opacity: 1; }
}

/* ---------- Collapsed navigation ---------- */
@media (max-width: 760px) {
  .hd-burger { display: inline-grid; }

  .hd-links {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    display: grid;
    gap: 2px;
    padding: 6px var(--hd-pad-x) 16px;
    background: var(--hd-panel);
    border-bottom: 1px solid var(--hd-line-soft);
    box-shadow: 0 14px 26px -18px rgba(0, 0, 0, 0.45);
    opacity: 0;
    visibility: hidden;
    transform: translateY(-10px);
    transition: opacity var(--hd-t) var(--hd-ease), transform var(--hd-t) var(--hd-ease),
      visibility var(--hd-t) var(--hd-ease);
  }
  .site-header.is-open .hd-links {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
  }
  .hd-links a {
    padding-block: 11px;
    font-size: 1rem;
    border-bottom: 1px solid var(--hd-line-soft);
  }
  .hd-links a:last-child { border-bottom: 0; }
  .hd-links a::after { display: none; }

  .hd-actions {
    margin-left: auto;
    padding-left: 0;
    border-left: 0;
  }
}

@media (max-width: 480px) {
  .hd-brand-name { display: none; }
  .hd-switch-opt { padding: 5px 10px; font-size: 0.64rem; }
  .hd-icon-btn { width: 32px; height: 32px; }
}

@media (prefers-reduced-motion: reduce) {
  .site-header,
  .site-header.is-hidden {
    transform: none;
    transition: none;
    animation: none;
  }
  .hd-switch-thumb,
  .hd-links a::after,
  .hd-burger-box span,
  .page-transition,
  .page-transition-mark,
  .page-transition-inner::before {
    transition: none;
    animation: none;
  }
}