:root{
  --back-to-top-size: 44px;
  --back-to-top-bg: rgba(17, 24, 39, 0.9);
  --back-to-top-bg-light: rgba(255, 255, 255, 0.95);
  --back-to-top-color: var(--md-accent-fg-color, #f59e0b);
  --back-to-top-shadow: 0 10px 15px -3px rgba(0,0,0,.1), 0 4px 6px -4px rgba(0,0,0,.1);
  --back-to-top-border: rgba(255, 255, 255, 0.2);
}

/* Button base */
.back-to-top {
  position: fixed;
  left: 50%;
  right: auto;
  bottom: calc(16px + env(safe-area-inset-bottom));
  width: var(--back-to-top-size);
  height: var(--back-to-top-size);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 9999px;
  background: var(--back-to-top-bg);
  color: var(--back-to-top-color) !important;
  border: 1px solid var(--back-to-top-border);
  box-shadow: var(--back-to-top-shadow);
  backdrop-filter: saturate(180%) blur(8px);
  -webkit-backdrop-filter: saturate(180%) blur(8px);
  opacity: 0;
  visibility: hidden;
  transform: translate(-50%, 10px) scale(0.98);
  transition: opacity .2s ease, transform .2s ease, visibility .2s ease, background .2s ease, color .2s ease;
  z-index: 13001; /* above header (12000) */
  pointer-events: auto;
  will-change: opacity, transform;
}

/* Visible state */
.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translate(-50%, 0) scale(1);
}


/* Icon */
.back-to-top svg {
  width: 26px;
  height: 26px;
  display: block;
  color: var(--back-to-top-color) !important;
}

/* Text icon styling (preferred) */
.back-to-top .back-to-top-icon {
  font-size: 22px;
  line-height: 1;
  display: inline-block;
  color: var(--back-to-top-color);
  font-weight: 900;
  text-shadow: 0 2px 6px rgba(245, 158, 11, 0.45);
}

/* Hide SVG fallback by default to avoid double icon */
.back-to-top .back-to-top-svg-fallback { display: none; }

/* Hover/active */
.back-to-top:hover {
  background: rgba(31, 41, 55, 0.8);
}
.back-to-top:active {
  transform: translateY(0) scale(0.98);
}

/* Focus ring */
.back-to-top:focus {
  outline: none;
  box-shadow: 0 0 0 3px rgba(245, 158, 11, 0.35), var(--back-to-top-shadow);
}

/* Respect reduced motion */
@media (prefers-reduced-motion: reduce) {
  .back-to-top {
    transition: none;
  }
}

/* Light/Dark scheme awareness via Material attribute */
html[data-md-color-scheme="default"] .back-to-top {
  background: var(--back-to-top-bg-light);
  color: var(--back-to-top-color);
  border-color: rgba(17, 24, 39, 0.08);
}

html[data-md-color-scheme="slate"] .back-to-top {
  background: var(--back-to-top-bg);
  color: var(--back-to-top-color);
  border-color: rgba(255, 255, 255, 0.12);
}

/* Ensure inner shapes also use currentColor in both themes */
.back-to-top svg path,
.back-to-top svg line,
.back-to-top svg polyline,
.back-to-top svg rect {
  stroke: currentColor;
  stroke-width: 2.25;
}

/* Filled caret uses theme accent via currentColor */
.back-to-top svg .filled {
  fill: currentColor !important;
  stroke: none !important;
}