:root {
  --soft-red: hsl(345, 95%, 68%);
  --grayish-blue: hsl(237, 18%, 59%);
  --card-bottom: hsl(236, 21%, 26%);
  --card-top: hsl(235, 20%, 22%);
  --page-top: hsl(234, 17%, 12%);
  --page-bottom: hsl(235, 16%, 14%);
  --white: hsl(0, 0%, 100%);
  --shadow: rgba(0, 0, 0, 0.3);
}

* {
  box-sizing: border-box;
}

html,
body {
  min-height: 100%;
}

body {
  margin: 0;
  font-family: "Red Hat Text", sans-serif;
  font-weight: 700;
  color: var(--white);
  background:
    url("./images/pattern-hills.svg") center bottom / 100% auto no-repeat,
    url("./images/bg-stars.svg") center top / cover no-repeat,
    linear-gradient(180deg, var(--page-top) 0%, var(--page-bottom) 100%);
  display: grid;
  place-items: center;
  padding: 2.5rem 1rem 1rem;
}

.countdown-app {
  width: min(46rem, 100%);
  min-height: 78vh;
  display: grid;
  align-content: space-between;
  justify-items: center;
  gap: 2.5rem;
}

.title {
  margin: 0;
  text-transform: uppercase;
  letter-spacing: 0.35em;
  text-align: center;
  font-size: clamp(1.05rem, 1.4vw + 0.8rem, 1.5rem);
}

.timer {
  width: 100%;
  display: grid;
  grid-template-columns: repeat(4, minmax(4.25rem, 1fr));
  gap: clamp(0.75rem, 2vw, 2rem);
}

.timer-segment {
  text-align: center;
}

.flip-card {
  position: relative;
  height: clamp(4.75rem, 12vw, 8.5rem);
  border-radius: 0.55rem;
  perspective: 720px;
  box-shadow: 0 0.6rem 0 0 #191a24;
  isolation: isolate;
}

.flip-card::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: linear-gradient(
    to bottom,
    rgba(255, 255, 255, 0.06),
    rgba(0, 0, 0, 0.12)
  );
  z-index: 2;
  pointer-events: none;
}

/* Side holes at the card's horizontal dividing line */
.flip-card::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 0;
  right: 0;
  height: 14px;
  transform: translateY(-50%);
  pointer-events: none;
  z-index: 6;
  background:
    radial-gradient(circle at center, var(--page-top) 47%, transparent 48%) -7px
      center / 14px 14px no-repeat,
    radial-gradient(circle at center, var(--page-top) 47%, transparent 48%)
      calc(100% + 7px) center / 14px 14px no-repeat;
}

.flip-static {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  overflow: hidden;
}

.half {
  display: block;
  position: absolute;
  left: 0;
  right: 0;
  height: 50%;
  overflow: hidden;
  background: var(--card-top);
}

.half-top {
  top: 0;
  border-bottom: 1px solid rgba(0, 0, 0, 0.35);
}

.half-bottom {
  bottom: 0;
  background: var(--card-bottom);
}

.number {
  position: absolute;
  left: 0;
  width: 100%;
  display: grid;
  place-items: center;
  color: var(--soft-red);
  font-size: clamp(2rem, 4.6vw, 4.8rem);
  letter-spacing: -0.06em;
  line-height: 1;
  font-variant-numeric: tabular-nums;
}

.half-top .number {
  top: 42%;
}

.half-bottom .number {
  top: -58%;
}

.flip-layer {
  position: absolute;
  left: 0;
  width: 100%;
  height: 50%;
  overflow: hidden;
  transform-style: preserve-3d;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  display: none;
  z-index: 3;
}

.flip-layer .number {
  text-shadow: 0 2px 6px var(--shadow);
}

.flip-top {
  top: 0;
  background: var(--card-top);
  transform-origin: bottom center;
  transform: rotateX(0deg);
  border-bottom: 1px solid rgba(0, 0, 0, 0.35);
}

.flip-top .number {
  top: 42%;
}

.flip-bottom {
  bottom: 0;
  background: var(--card-bottom);
  transform-origin: top center;
  transform: rotateX(90deg);
}

.flip-bottom .number {
  top: -58%;
}

.flip-card.is-flipping .flip-layer {
  display: block;
}

.flip-card.is-flipping .flip-top {
  animation: flipTop 0.34s ease-in forwards;
}

.flip-card.is-flipping .flip-bottom {
  animation: flipBottom 0.34s ease-out 0.34s both;
}

.segment-label {
  margin: 1rem 0 0;
  color: var(--grayish-blue);
  text-transform: uppercase;
  letter-spacing: 0.35em;
  font-size: clamp(0.5rem, 1vw, 0.8rem);
}

.social-links {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  gap: 2rem;
}

.social-links a {
  display: inline-grid;
  place-items: center;
}

.social-links a img {
  display: block;
  transition: filter 180ms ease;
}

.social-links a:hover img,
.social-links a:focus-visible img {
  filter: brightness(0) saturate(100%) invert(60%) sepia(74%) saturate(1585%)
    hue-rotate(304deg) brightness(106%) contrast(96%);
}

.attribution {
  margin-top: 1.75rem;
  font-size: 0.6875rem;
  text-align: center;
  color: var(--grayish-blue);
}

.attribution a {
  color: var(--soft-red);
}

.sr-only {
  border: 0;
  clip-path: inset(50%);
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0;
  position: absolute;
  white-space: nowrap;
  width: 1px;
}

@keyframes flipTop {
  from {
    transform: rotateX(0deg);
  }

  to {
    transform: rotateX(-90deg);
  }
}

@keyframes flipBottom {
  from {
    transform: rotateX(90deg);
  }

  to {
    transform: rotateX(0deg);
  }
}

@media (max-width: 37.5em) {
  body {
    padding-top: 5.5rem;
  }

  .timer {
    gap: 0.7rem;
  }

  .flip-card {
    border-radius: 0.4rem;
  }

  .segment-label {
    letter-spacing: 0.22em;
  }

  .social-links {
    gap: 1.8rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  html:not(.force-motion) *,
  html:not(.force-motion) *::before,
  html:not(.force-motion) *::after {
    animation-duration: 1ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 1ms !important;
    scroll-behavior: auto !important;
  }
}