.back-to-top {
  --_bg: var(--back-to-top-bg, #000000);
  --_color: var(--back-to-top-color, #FFFFFF);
  --_size: var(--back-to-top-size, 48px);
  --_bottom: var(--back-to-top-bottom, 30px);
  --_right: var(--back-to-top-right, 30px);

  position: fixed;
  bottom: var(--_bottom);
  right: var(--_right);
  z-index: 999;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity 0.3s ease, visibility 0.3s ease, transform 0.3s ease;
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top__button {
  display: flex;
  align-items: center;
  justify-content: center;
  width: var(--_size);
  height: var(--_size);
  padding: 0;
  background-color: var(--_bg);
  color: var(--_color);
  border: none;
  cursor: pointer;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
  transition: transform 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease;
}

/* Shape variants */
.back-to-top--circle .back-to-top__button {
  border-radius: 50%;
}

.back-to-top--rounded .back-to-top__button {
  border-radius: 8px;
}

.back-to-top--square .back-to-top__button {
  border-radius: 0;
}

.back-to-top__button:hover {
  transform: scale(1.1);
  box-shadow: 0 6px 16px rgba(0, 0, 0, 0.2);
}

.back-to-top__button:active {
  transform: scale(0.95);
}

.back-to-top__button svg {
  width: calc(var(--_size) * 0.5);
  height: calc(var(--_size) * 0.5);
}

@media (max-width: 749px) {
  .back-to-top {
    --_size: calc(var(--back-to-top-size, 48px) * 0.85);
    --_bottom: calc(var(--back-to-top-bottom, 30px) * 0.7);
    --_right: calc(var(--back-to-top-right, 30px) * 0.7);
  }
}