:root {
  color-scheme: dark;
  --ink: #12071d;
  --midnight: #2a0d3a;
  --purple: #5a1b73;
  --purple-soft: #a44ab4;
  --paper: #f6efe2;
  --gold: #d6ad53;
  --gold-soft: #f1cf7a;
  --card-ratio: 1.600338696;
  --card-width: min(76vw, calc(78vh * var(--card-ratio)), 1060px);
  --envelope-width: min(52vw, calc(54vh * var(--card-ratio)), 730px);
}

* {
  box-sizing: border-box;
}

html,
body {
  width: 100%;
  min-height: 100%;
  margin: 0;
}

body {
  overflow: hidden;
  font-family:
    "PingFang SC",
    "Hiragino Sans GB",
    "Microsoft YaHei",
    system-ui,
    sans-serif;
  background:
    linear-gradient(180deg, rgba(18, 7, 29, 0.24), rgba(18, 7, 29, 0.9)),
    radial-gradient(60% 70% at 74% 24%, rgba(164, 74, 180, 0.24), transparent 62%),
    radial-gradient(48% 64% at 16% 78%, rgba(214, 173, 83, 0.1), transparent 68%),
    linear-gradient(135deg, #3b1555 0%, #160820 48%, #542062 100%);
  color: var(--paper);
}

button {
  padding: 0;
  border: 0;
  color: inherit;
  font: inherit;
  background: transparent;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}

button:focus-visible {
  outline: 2px solid rgba(241, 207, 122, 0.88);
  outline-offset: 8px;
}

.scene {
  position: relative;
  display: grid;
  width: 100vw;
  height: 100vh;
  min-height: 460px;
  place-items: center;
  overflow: hidden;
}

.scene::before {
  position: absolute;
  inset: 8vmin;
  border: 1px solid rgba(241, 207, 122, 0.22);
  content: "";
  pointer-events: none;
}

.stage {
  position: relative;
  display: grid;
  width: 100%;
  height: 100%;
  place-items: center;
  perspective: 1900px;
  isolation: isolate;
}

.hint {
  position: absolute;
  bottom: clamp(24px, 6vh, 64px);
  left: 50%;
  margin: 0;
  padding: 0;
  color: rgba(244, 239, 230, 0.82);
  font-size: clamp(13px, 1.25vw, 17px);
  letter-spacing: 0;
  text-align: center;
  text-shadow: 0 2px 18px rgba(0, 0, 0, 0.48);
  transform: translateX(-50%);
  transition:
    opacity 360ms ease,
    transform 360ms ease;
}

.card {
  position: absolute;
  z-index: 1;
  width: var(--card-width);
  aspect-ratio: 1890 / 1181;
  border-radius: 9px;
  opacity: 0;
  pointer-events: none;
  transform: translate3d(0, 18vh, -120px) scale(0.46);
  transform-style: preserve-3d;
  transition:
    opacity 520ms ease,
    transform 1350ms cubic-bezier(0.18, 0.82, 0.22, 1);
}

.card-inner {
  position: absolute;
  inset: 0;
  display: block;
  border-radius: inherit;
  box-shadow:
    0 24px 80px rgba(0, 0, 0, 0.44),
    0 0 0 1px rgba(241, 207, 122, 0.18);
  transform-style: preserve-3d;
  transition: transform 950ms cubic-bezier(0.22, 0.64, 0.26, 1);
}

.card-face {
  position: absolute;
  inset: 0;
  display: block;
  width: 100%;
  height: 100%;
  border-radius: inherit;
  object-fit: contain;
  background: #12071d;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.card-back {
  transform: rotateY(180deg);
}

.stage.is-open .card {
  opacity: 1;
  transform: translate3d(0, -3vh, 150px) scale(1);
}

.stage.is-ready .card {
  pointer-events: auto;
}

.stage.is-flipped .card-inner {
  transform: rotateY(180deg);
}

.envelope {
  position: absolute;
  z-index: 2;
  width: var(--envelope-width);
  aspect-ratio: 1.62 / 1;
  isolation: isolate;
  transform: translate3d(0, 6vh, 0);
  transform-style: preserve-3d;
  transition:
    opacity 520ms ease 780ms,
    transform 1050ms cubic-bezier(0.2, 0.72, 0.25, 1) 260ms;
}

.envelope-shadow {
  position: absolute;
  z-index: 0;
  right: 9%;
  bottom: -15%;
  left: 9%;
  height: 18%;
  border-radius: 999px;
  background: rgba(0, 0, 0, 0.34);
  filter: blur(18px);
  transform: translateZ(-2px);
}

.envelope-back {
  position: absolute;
  z-index: 2;
  inset: 6% 0 0;
  border-radius: 6px;
  background:
    linear-gradient(150deg, rgba(255, 255, 255, 0.16), transparent 38%),
    linear-gradient(180deg, #6c2b80 0%, #321141 100%);
  box-shadow:
    inset 0 0 0 1px rgba(241, 207, 122, 0.28),
    0 18px 58px rgba(0, 0, 0, 0.34);
}

.envelope-letter-edge {
  position: absolute;
  z-index: 1;
  top: 3%;
  right: 8%;
  left: 8%;
  height: 24%;
  border-radius: 5px 5px 0 0;
  background: linear-gradient(180deg, #fbf0dc 0%, #ddba68 100%);
  box-shadow: inset 0 -1px 0 rgba(111, 55, 36, 0.28);
}

.envelope-pocket {
  position: absolute;
  z-index: 3;
  inset: 34% 0 0;
  border-radius: 0 0 7px 7px;
  overflow: hidden;
  background: linear-gradient(180deg, #5f236e 0%, #2a0d3a 100%);
  clip-path: polygon(0 0, 50% 62%, 100% 0, 100% 100%, 0 100%);
}

.envelope-pocket::before,
.envelope-pocket::after {
  position: absolute;
  inset: 0;
  content: "";
}

.envelope-pocket::before {
  background: linear-gradient(35deg, rgba(241, 207, 122, 0.22), transparent 48%);
  clip-path: polygon(0 0, 50% 62%, 0 100%);
}

.envelope-pocket::after {
  background: linear-gradient(-35deg, rgba(18, 7, 29, 0.42), transparent 50%);
  clip-path: polygon(100% 0, 50% 62%, 100% 100%);
}

.envelope-flap {
  position: absolute;
  inset: 6% 0 34%;
  z-index: 4;
  border-radius: 7px 7px 0 0;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.14), transparent 44%),
    linear-gradient(160deg, #7c338f 0%, #341144 100%);
  clip-path: polygon(0 0, 100% 0, 50% 100%);
  transform-origin: 50% 0%;
  transition: transform 860ms cubic-bezier(0.18, 0.72, 0.18, 1);
}

.envelope-seal {
  position: absolute;
  top: 56%;
  left: 50%;
  z-index: 5;
  width: 10.5%;
  aspect-ratio: 1;
  border-radius: 50%;
  background:
    radial-gradient(circle at 35% 30%, rgba(255, 255, 255, 0.46), transparent 30%),
    linear-gradient(150deg, #f1cf7a, #a36e24);
  box-shadow:
    0 5px 12px rgba(0, 0, 0, 0.24),
    inset 0 0 0 1px rgba(255, 255, 255, 0.26);
  transform: translate(-50%, -50%);
  transition:
    opacity 280ms ease,
    transform 440ms ease;
}

.stage.is-open .envelope {
  opacity: 0;
  pointer-events: none;
  transform: translate3d(0, 24vh, -220px) scale(0.92);
}

.stage.is-open .envelope-flap {
  transform: rotateX(168deg);
}

.stage.is-open .envelope-seal {
  opacity: 0;
  transform: translate(-50%, -50%) scale(0.72);
}

.stage.is-flipped .hint {
  opacity: 0;
  transform: translate(-50%, 12px);
}

.orientation-lock {
  position: fixed;
  inset: 0;
  z-index: 20;
  display: none;
  place-items: center;
  padding: 28px;
  background:
    linear-gradient(180deg, rgba(18, 7, 29, 0.88), rgba(18, 7, 29, 0.96)),
    #12071d;
}

.orientation-lock p {
  margin: 0;
  color: var(--paper);
  font-size: clamp(22px, 8vw, 34px);
  letter-spacing: 0;
  text-align: center;
}

@media (hover: none) and (pointer: coarse) and (orientation: portrait) {
  .orientation-lock {
    display: grid;
  }
}

@media (max-width: 900px) and (orientation: landscape) {
  :root {
    --card-width: min(82vw, calc(74vh * var(--card-ratio)), 920px);
    --envelope-width: min(58vw, calc(52vh * var(--card-ratio)), 640px);
  }

  .scene {
    min-height: 300px;
  }

  .hint {
    bottom: clamp(14px, 4vh, 28px);
  }

  .stage.is-open .card {
    transform: translate3d(0, -2vh, 150px) scale(1);
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 1ms !important;
    animation-duration: 1ms !important;
  }
}