.back-to-top {
 position: fixed;
 z-index: 40;
 right: max(1rem, env(safe-area-inset-right));
 bottom: calc(1rem + env(safe-area-inset-bottom));
 display: grid;
 place-items: center;
 width: 3.25rem;
 height: 3.25rem;
 padding: 0;
 border: 2px solid var(--color-secondary);
 border-radius: 50%;
 background: var(--color-secondary);
 color: #fff;
 font-size: 2rem;
 line-height: 1;
 box-shadow: 0 3px 12px rgb(0 0 0 / 20%);
 cursor: pointer;
 transition: background-color var(--transition-fast), color var(--transition-fast);
}
.back-to-top[hidden] { display: none; }
.back-to-top:hover { background: #262626; color: #fff; }
.back-to-top:active { transform: translateY(1px); }
.back-to-top:focus-visible { outline: 3px solid var(--color-secondary); outline-offset: 4px; }
/* The mobile header has a free centre slot: keep the control off reading/cards. */
@media (max-width: 74.9375rem) {
 .site-header--home .site-header__brand { flex: 0 0 auto; width: min(18rem, calc(50vw - 3.75rem)); }
 .site-header--home .site-header__brand img { max-width: 100%; }
 .back-to-top {
  top: .75rem;
  bottom: auto;
  right: auto;
  left: 50%;
  width: 2.75rem;
  height: 2.75rem;
  transform: translateX(-50%);
 }
 .back-to-top:active { transform: translate(-50%, 1px); }
 .admin-bar .back-to-top { top: calc(46px + .75rem); }
}