/* Back to top — water ripple button */

.btt {
  position: fixed;
  right: 1.25rem;
  bottom: 1.25rem;
  z-index: 45;
  width: 3.25rem;
  height: 3.25rem;
  padding: 0;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  overflow: hidden;
  background: #0b1e3a;
  box-shadow:
    0 14px 32px -12px rgb(11 30 58 / 0.45),
    0 0 0 1px rgb(255 255 255 / 0.08) inset;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translate3d(0, 0.75rem, 0) scale(0.92);
  transition:
    opacity 0.4s cubic-bezier(0.16, 1, 0.3, 1),
    transform 0.4s cubic-bezier(0.16, 1, 0.3, 1),
    visibility 0.4s,
    box-shadow 0.25s ease;
}

.btt.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translate3d(0, 0, 0) scale(1);
}

.btt:hover {
  box-shadow:
    0 18px 36px -10px rgb(11 30 58 / 0.5),
    0 0 0 1px rgb(255 255 255 / 0.12) inset;
}

.btt:focus-visible {
  outline: 2px solid #ff7a00;
  outline-offset: 3px;
}

.btt__shine {
  position: absolute;
  inset: 0;
  z-index: 0;
  background: radial-gradient(circle at 30% 20%, rgb(255 255 255 / 0.14), transparent 55%);
  pointer-events: none;
}

.btt__waves {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 1;
  height: 58%;
  overflow: hidden;
  pointer-events: none;
}

.btt__wave {
  position: absolute;
  left: -60%;
  bottom: -35%;
  width: 220%;
  height: 220%;
  border-radius: 42%;
  background: linear-gradient(
    180deg,
    rgb(18 183 106 / 0.55) 0%,
    rgb(56 189 248 / 0.4) 45%,
    rgb(255 122 0 / 0.25) 100%
  );
  animation: btt-wave-drift 5.5s ease-in-out infinite;
  will-change: transform;
}

.btt__wave--2 {
  left: -40%;
  bottom: -45%;
  opacity: 0.85;
  animation-name: btt-wave-drift-alt;
  animation-duration: 7s;
  animation-delay: -2.5s;
}

.btt__wave--3 {
  left: -50%;
  bottom: -50%;
  height: 180%;
  opacity: 0.5;
  background: linear-gradient(
    180deg,
    rgb(255 255 255 / 0.2) 0%,
    rgb(18 183 106 / 0.35) 100%
  );
  animation-duration: 6s;
  animation-delay: -1s;
}

@keyframes btt-wave-drift {
  0%,
  100% {
    transform: translate3d(0, 0, 0) rotate(0deg);
  }
  50% {
    transform: translate3d(-6%, 2%, 0) rotate(4deg);
  }
}

@keyframes btt-wave-drift-alt {
  0%,
  100% {
    transform: translate3d(0, 0, 0) rotate(0deg);
  }
  50% {
    transform: translate3d(5%, 3%, 0) rotate(-3deg);
  }
}

.btt__icon {
  position: relative;
  z-index: 2;
  display: grid;
  place-items: center;
  height: 100%;
  color: #fff;
  transform: translateY(-2px);
  transition: transform 0.25s ease;
}

.btt:hover .btt__icon {
  transform: translateY(-5px);
}

.btt__icon svg {
  width: 1.25rem;
  height: 1.25rem;
  filter: drop-shadow(0 1px 2px rgb(0 0 0 / 0.2));
}

.btt__ripple {
  position: absolute;
  inset: 0;
  z-index: 3;
  border-radius: 50%;
  pointer-events: none;
  opacity: 0;
  background: radial-gradient(circle, rgb(255 255 255 / 0.35) 0%, transparent 70%);
  transform: scale(0.4);
}

.btt.is-ripple .btt__ripple {
  animation: btt-ripple 0.65s ease-out forwards;
}

@keyframes btt-ripple {
  0% {
    opacity: 0.6;
    transform: scale(0.4);
  }
  100% {
    opacity: 0;
    transform: scale(1.35);
  }
}

@media (min-width: 640px) {
  .btt {
    right: 1.75rem;
    bottom: 1.75rem;
    width: 3.5rem;
    height: 3.5rem;
  }

  .btt__icon svg {
    width: 1.35rem;
    height: 1.35rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .btt,
  .btt__wave,
  .btt__icon {
    transition: none;
    animation: none !important;
  }

  .btt.is-visible {
    transform: none;
  }
}