/* ==========================================================================
   Scroll To Top — World-class 3D FAB + scroll progress ring
   ========================================================================== */

.scroll-top {
  --st-progress: 0;
  --st-tilt-x: 0deg;
  --st-tilt-y: 0deg;
  --st-lift: 0px;
  --st-glow: 0.55;

  position: fixed;
  right: max(18px, env(safe-area-inset-right));
  bottom: max(18px, env(safe-area-inset-bottom));
  z-index: var(--z-toast);
  width: 56px;
  height: 56px;
  padding: 0;
  border: 0;
  border-radius: 18px;
  background: transparent;
  color: var(--color-primary-dark);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translate3d(0, 20px, 0) scale(0.88);
  pointer-events: none;
  perspective: 900px;
  transform-style: preserve-3d;
  will-change: transform, opacity;
  transition:
    opacity 0.35s var(--ease-out-expo),
    visibility 0.35s,
    transform 0.45s var(--ease-out-expo);
}

.scroll-top.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

.scroll-top.is-visible:not(.is-entered) {
  animation: scrollTopEnter 0.55s var(--ease-out-expo) forwards;
}

.scroll-top.is-entered {
  transform:
    translate3d(0, var(--st-lift), 0)
    scale(1)
    rotateX(var(--st-tilt-y))
    rotateY(var(--st-tilt-x));
}

.scroll-top.is-launching .scroll-top__arrow {
  animation: scrollTopArrowLaunch 0.65s var(--ease-out-expo);
}

.scroll-top.is-launching .scroll-top__chev {
  animation: scrollTopChevLaunch 0.65s var(--ease-out-expo);
}

.scroll-top:focus-visible {
  outline: 3px solid rgba(var(--color-primary-rgb), 0.35);
  outline-offset: 4px;
}

/* 3D stage */
.scroll-top__stage {
  position: relative;
  display: block;
  width: 100%;
  height: 100%;
  border-radius: inherit;
  transform-style: preserve-3d;
  transform: translateZ(0);
}

/* Infinite background rings (subtle, premium) */
.scroll-top__stage::before,
.scroll-top__stage::after {
  content: "";
  position: absolute;
  inset: -20%;
  border-radius: 999px;
  pointer-events: none;
  z-index: 0;
  opacity: 0;
  transform: translateZ(-10px) scale(0.75);
  filter: blur(0px);
  transition: opacity 0.25s ease;
}

.scroll-top__stage::before {
  background:
    radial-gradient(closest-side, transparent 72%, rgba(16, 185, 129, 0.22) 74%, transparent 78%),
    radial-gradient(closest-side, transparent 56%, rgba(251, 191, 36, 0.16) 58%, transparent 62%),
    radial-gradient(closest-side, transparent 38%, rgba(59, 130, 246, 0.12) 40%, transparent 44%);
  animation: scrollTopRings 2.6s linear infinite;
}

.scroll-top__stage::after {
  inset: -28%;
  background:
    radial-gradient(closest-side, transparent 66%, rgba(255, 255, 255, 0.65) 68%, transparent 72%),
    radial-gradient(closest-side, transparent 46%, rgba(16, 185, 129, 0.14) 48%, transparent 52%);
  animation: scrollTopRings 3.4s linear infinite reverse;
}

.scroll-top.is-visible .scroll-top__stage::before,
.scroll-top.is-visible .scroll-top__stage::after {
  opacity: 0.9;
}

.scroll-top.is-hovered .scroll-top__stage::before,
.scroll-top.is-hovered .scroll-top__stage::after {
  opacity: 1;
  filter: saturate(1.08);
}

/* Scroll progress ring */
.scroll-top__progress {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  transform: rotate(-90deg);
  pointer-events: none;
  z-index: 0;
}

.scroll-top__progress-track {
  fill: none;
  stroke: rgba(148, 163, 184, 0.22);
  stroke-width: 2.5;
}

.scroll-top__progress-fill {
  fill: none;
  stroke: var(--color-primary);
  stroke-width: 2.75;
  stroke-linecap: round;
  stroke-dasharray: 1;
  stroke-dashoffset: calc(1 - var(--st-progress));
  filter: drop-shadow(0 0 6px rgba(var(--color-primary-rgb), 0.35));
  transition: stroke-dashoffset 0.08s linear;
}

.scroll-top__glow {
  position: absolute;
  inset: -14px;
  border-radius: 24px;
  background:
    radial-gradient(circle at 30% 25%, rgba(16, 185, 129, calc(0.32 * var(--st-glow))), transparent 58%),
    radial-gradient(circle at 75% 80%, rgba(251, 191, 36, calc(0.22 * var(--st-glow))), transparent 55%);
  filter: blur(16px);
  opacity: calc(0.5 + var(--st-progress) * 0.5);
  transform: translateZ(-8px) scale(calc(0.95 + var(--st-progress) * 0.08));
  pointer-events: none;
  transition: opacity 0.2s ease;
}

.scroll-top__ring {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  pointer-events: none;
  background: linear-gradient(
    145deg,
    rgba(255, 255, 255, 0.95) 0%,
    rgba(236, 253, 245, 0.75) 45%,
    rgba(255, 251, 235, 0.65) 100%
  );
  border: 1px solid rgba(255, 255, 255, 0.85);
  box-shadow:
    0 1px 0 rgba(255, 255, 255, 0.9) inset,
    0 18px 40px rgba(15, 23, 42, 0.12),
    0 4px 12px rgba(15, 23, 42, 0.06);
  transform: translateZ(4px);
  z-index: 1;
}

.scroll-top__body {
  position: absolute;
  inset: 3px;
  border-radius: 15px;
  display: grid;
  place-items: center;
  background: rgba(255, 255, 255, 0.72);
  -webkit-backdrop-filter: blur(14px);
  backdrop-filter: blur(14px);
  transform: translateZ(12px);
  z-index: 2;
  overflow: hidden;
  transition:
    background 0.25s ease,
    box-shadow 0.25s ease;
}

.scroll-top__shine {
  position: absolute;
  inset: -40%;
  background: linear-gradient(
    115deg,
    transparent 35%,
    rgba(255, 255, 255, 0.75) 48%,
    transparent 62%
  );
  transform: translateX(-120%) rotate(12deg);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.25s ease;
}

.scroll-top.is-hovered .scroll-top__shine {
  opacity: 1;
  animation: scrollTopShine 1.8s ease-in-out infinite;
}

.scroll-top__icon {
  position: relative;
  z-index: 1;
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  transform: translateZ(18px);
}

.scroll-top__icon svg {
  width: 22px;
  height: 22px;
  display: block;
}

.scroll-top__arrow,
.scroll-top__chev {
  transition: transform 0.2s var(--ease-out-expo);
}

.scroll-top.is-hovered .scroll-top__arrow {
  transform: translateY(-1px);
}

.scroll-top.is-hovered .scroll-top__chev--l {
  transform: translate(-1px, -1px);
}

.scroll-top.is-hovered .scroll-top__chev--r {
  transform: translate(1px, -1px);
}

.scroll-top.is-hovered .scroll-top__body {
  background: rgba(255, 255, 255, 0.88);
  box-shadow: 0 8px 24px rgba(var(--color-primary-rgb), 0.12);
}

.scroll-top.is-hovered {
  --st-glow: 1;
}

.scroll-top:active .scroll-top__body {
  transform: translateZ(8px) scale(0.96);
}

/* Keyframes */
@keyframes scrollTopEnter {
  0% {
    opacity: 0;
    transform: translate3d(0, 24px, 0) scale(0.82) rotateX(12deg);
  }
  70% {
    opacity: 1;
    transform: translate3d(0, -4px, 0) scale(1.04) rotateX(-4deg);
  }
  100% {
    opacity: 1;
    transform: translate3d(0, 0, 0) scale(1) rotateX(0deg);
  }
}

@keyframes scrollTopShine {
  0% { transform: translateX(-120%) rotate(12deg); }
  100% { transform: translateX(120%) rotate(12deg); }
}

@keyframes scrollTopArrowLaunch {
  0% { transform: translateY(0); opacity: 1; }
  40% { transform: translateY(-6px); opacity: 1; }
  100% { transform: translateY(-14px); opacity: 0; }
}

@keyframes scrollTopChevLaunch {
  0% { transform: translate(0, 0); opacity: 1; }
  50% { transform: translate(0, -3px); opacity: 0.9; }
  100% { transform: translate(0, -8px); opacity: 0; }
}

@keyframes scrollTopRings {
  0% { transform: translateZ(-10px) scale(0.72) rotate(0deg); }
  50% { transform: translateZ(-10px) scale(0.88) rotate(180deg); }
  100% { transform: translateZ(-10px) scale(0.72) rotate(360deg); }
}

@media (max-width: 640px) {
  .scroll-top {
    width: 50px;
    height: 50px;
    border-radius: 16px;
  }

  .scroll-top__body {
    inset: 2px;
    border-radius: 14px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .scroll-top,
  .scroll-top.is-visible:not(.is-entered) {
    animation: none;
    transition: opacity 0.2s ease, visibility 0.2s;
  }

  .scroll-top.is-entered {
    transform: none;
  }

  .scroll-top__shine,
  .scroll-top.is-launching .scroll-top__arrow,
  .scroll-top.is-launching .scroll-top__chev {
    animation: none !important;
  }

  .scroll-top__stage::before,
  .scroll-top__stage::after {
    animation: none !important;
  }

  .scroll-top__progress-fill {
    transition: none;
  }
}