/* Two things that react to scrolling: the reveal animation and the
   "back to top" button. */

/* --- Scroll reveal --- */

/* js/reveal.js adds "reveal-wait" to blocks below the screen and swaps it
   for "reveal-in" when they scroll into view. */
.reveal-wait {
  opacity: 0;
}

/* The keyframes only have a "from" part, so the block animates to its normal
   look and nothing is left behind (hover effects keep working). */
.reveal-in {
  animation: reveal-in 0.6s ease backwards;
}

@keyframes reveal-in {
  from {
    opacity: 0;
    transform: translateY(1.25rem);
  }
}

/* Cards that sit in one row come in one after another. */
.reveal-in:nth-child(3n + 2) {
  animation-delay: 0.08s;
}

.reveal-in:nth-child(3n) {
  animation-delay: 0.16s;
}

/* On paper nothing may stay hidden. */
@media print {
  .reveal-wait {
    opacity: 1;
  }
}

/* --- Back to top --- */

.back-to-top {
  position: fixed;
  right: var(--space-4);
  bottom: var(--space-4);
  z-index: 15;
  display: grid;
  place-items: center;
  width: 3rem;
  height: 3rem;
  border-radius: 50%;
  background: var(--color-brand);
  color: var(--color-on-brand);
  box-shadow: var(--shadow-md);
  /* Hidden at first. "visibility: hidden" also takes it out of the Tab order,
     so keyboard users cannot land on a button they cannot see. */
  opacity: 0;
  visibility: hidden;
  transform: translateY(0.5rem);
  transition: opacity 0.2s ease, transform 0.2s ease, visibility 0.2s;
}

/* js/back-to-top.js adds this class after the page is scrolled down. */
.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: none;
}

.back-to-top:hover {
  background: var(--color-brand-strong);
  color: var(--color-on-brand);
}