:root {
  --bg-top: #fff8fa;
  --bg-bottom: #f8fbff;
  --ink: #4c3844;
  --muted: #8d6f7d;
  --rose: #e994a9;
  --rose-deep: #b95d76;
  --paper: #fffdf8;
  --paper-edge: #efd9dc;
  --shadow: 0 24px 70px rgba(166, 83, 112, 0.2);
  color-scheme: light;
  font-family: "Microsoft YaHei", "PingFang SC", "Hiragino Sans GB", Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

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

body {
  background:
    radial-gradient(circle at 50% 34%, rgba(255, 255, 255, 0.92), transparent 23rem),
    radial-gradient(circle at 16% 16%, rgba(255, 230, 238, 0.86), transparent 28rem),
    radial-gradient(circle at 84% 12%, rgba(228, 245, 255, 0.86), transparent 25rem),
    linear-gradient(155deg, var(--bg-top), var(--bg-bottom));
  color: var(--ink);
  overflow-x: hidden;
}

button {
  font: inherit;
  -webkit-tap-highlight-color: transparent;
}

.page-shell {
  position: relative;
  display: grid;
  min-height: 100vh;
  min-height: 100svh;
  place-items: center;
  padding: 28px 16px;
  isolation: isolate;
}

.page-shell::before {
  position: fixed;
  inset: 0;
  z-index: -2;
  content: "";
  background-image:
    linear-gradient(rgba(255, 255, 255, 0.42) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.34) 1px, transparent 1px);
  background-size: 38px 38px;
  mask-image: linear-gradient(to bottom, rgba(0, 0, 0, 0.42), transparent);
}

.petal-field {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  overflow: hidden;
}

.petal {
  position: absolute;
  top: -36px;
  left: var(--x);
  width: var(--size);
  height: calc(var(--size) * 0.74);
  border-radius: 100% 0 100% 0;
  background: linear-gradient(135deg, rgba(255, 177, 198, 0.86), rgba(255, 231, 237, 0.42));
  opacity: var(--opacity);
  transform: rotate(var(--rotate));
  animation: petal-fall var(--duration) linear var(--delay) infinite;
}

.petal--1 {
  filter: blur(0.2px);
}

.petal--2 {
  background: linear-gradient(135deg, rgba(255, 205, 216, 0.72), rgba(255, 246, 248, 0.42));
}

@keyframes petal-fall {
  0% {
    translate: 0 -8vh;
    rotate: 0deg;
  }

  50% {
    translate: var(--drift) 52vh;
    rotate: 190deg;
  }

  100% {
    translate: calc(var(--drift) * -0.55) 108vh;
    rotate: 370deg;
  }
}

.letter-stage {
  display: grid;
  width: min(100%, 680px);
  min-height: 660px;
  place-items: center;
}

.envelope-scene {
  position: relative;
  display: grid;
  width: min(94vw, 620px);
  min-height: 620px;
  place-items: center;
  perspective: 1300px;
}

.cover-panel {
  position: relative;
  z-index: 2;
  display: grid;
  justify-items: center;
  gap: 24px;
  transform-style: preserve-3d;
  transition:
    opacity 420ms ease,
    transform 700ms cubic-bezier(0.2, 0.85, 0.2, 1);
}

.envelope {
  position: relative;
  width: min(92vw, 560px);
  aspect-ratio: 1.5;
  padding: 0;
  border: 0;
  background: transparent;
  cursor: pointer;
  filter: drop-shadow(var(--shadow));
  transform-style: preserve-3d;
  transition:
    transform 760ms cubic-bezier(0.2, 0.85, 0.2, 1),
    filter 260ms ease;
}

.envelope:hover {
  filter: drop-shadow(0 30px 76px rgba(166, 83, 112, 0.26));
}

.envelope:focus-visible,
.icon-button:focus-visible,
.primary-button:focus-visible,
.secondary-button:focus-visible {
  outline: 3px solid rgba(201, 95, 125, 0.5);
  outline-offset: 5px;
}

.envelope__face,
.envelope__base,
.envelope__left,
.envelope__right,
.envelope__bottom,
.envelope__flap,
.envelope__back-panel,
.envelope__back-flap {
  position: absolute;
  inset: 0;
}

.envelope__face {
  border-radius: 12px;
  backface-visibility: hidden;
  overflow: hidden;
  transform-style: preserve-3d;
  transition:
    opacity 260ms ease,
    transform 760ms cubic-bezier(0.2, 0.85, 0.2, 1);
}

.envelope__face::before {
  position: absolute;
  inset: 0;
  z-index: 6;
  content: "";
  pointer-events: none;
  background:
    radial-gradient(circle at 18% 22%, rgba(255, 255, 255, 0.34), transparent 5.5rem),
    linear-gradient(135deg, rgba(255, 255, 255, 0.18), transparent 46%, rgba(185, 93, 118, 0.08));
  mix-blend-mode: soft-light;
}

.envelope__face--front {
  background:
    linear-gradient(135deg, rgba(255, 255, 255, 0.18), transparent 34%),
    radial-gradient(circle at 68% 26%, rgba(255, 255, 255, 0.34), transparent 9rem),
    linear-gradient(145deg, #ffd3dc, #f59db5 72%);
  box-shadow:
    inset 0 0 0 1px rgba(176, 71, 104, 0.12),
    inset 0 14px 24px rgba(255, 255, 255, 0.22);
  transform: rotateY(0deg);
}

.envelope__face--back {
  display: grid;
  place-items: center;
  background:
    radial-gradient(circle at 50% 42%, rgba(255, 255, 255, 0.32), transparent 8rem),
    linear-gradient(145deg, #ffd8e1, #f3a1b7);
  box-shadow: inset 0 0 0 1px rgba(176, 71, 104, 0.1);
  opacity: 0;
  transform: rotateY(-180deg);
}

.envelope__base {
  z-index: 1;
  background: linear-gradient(145deg, #ffdbe4, #f5a2b8);
}

.envelope__address {
  position: absolute;
  top: 25%;
  right: 11%;
  left: 11%;
  z-index: 5;
  display: grid;
  justify-items: center;
  gap: 12px;
  color: var(--rose-deep);
  pointer-events: none;
  transition:
    opacity 260ms ease,
    transform 360ms ease;
}

.envelope__postmark {
  justify-self: start;
  padding: 4px 11px;
  border: 1px solid rgba(185, 93, 118, 0.32);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.18);
  color: rgba(185, 93, 118, 0.78);
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(0.7rem, 1.7vw, 0.86rem);
  letter-spacing: 0.08em;
  line-height: 1;
  text-transform: uppercase;
  transform: rotate(-7deg);
}

.envelope__seal {
  position: relative;
  z-index: 4;
  width: clamp(58px, 10vw, 82px);
  height: clamp(58px, 10vw, 82px);
  filter: drop-shadow(0 10px 22px rgba(185, 93, 118, 0.24));
}

.envelope__to {
  font-family: Georgia, "Times New Roman", serif;
  width: 100%;
  color: #a94763;
  font-size: clamp(2.1rem, 6.8vw, 3.95rem);
  font-weight: 700;
  line-height: 1;
  text-align: center;
  text-shadow:
    0 2px 0 rgba(255, 255, 255, 0.34),
    0 10px 26px rgba(185, 93, 118, 0.12);
  overflow-wrap: anywhere;
}

.envelope__line {
  width: min(72%, 270px);
  height: 2px;
  border-radius: 999px;
  background: linear-gradient(90deg, transparent, rgba(185, 93, 118, 0.42), transparent);
}

.envelope__hint {
  position: relative;
  z-index: 4;
  align-self: end;
  margin-bottom: 20%;
  padding: 7px 16px;
  border: 1px solid rgba(185, 93, 118, 0.18);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.24);
  color: var(--muted);
  font-size: clamp(0.86rem, 2.8vw, 1rem);
}

.envelope__left {
  z-index: 2;
  clip-path: polygon(0 0, 52% 50%, 0 100%);
  border-radius: 8px;
  background: linear-gradient(105deg, #ffcbd7, #f5adbd);
}

.envelope__right {
  z-index: 2;
  clip-path: polygon(100% 0, 48% 50%, 100% 100%);
  border-radius: 8px;
  background: linear-gradient(255deg, #ffcbd7, #f6acbe);
}

.envelope__bottom {
  z-index: 3;
  clip-path: polygon(0 100%, 50% 42%, 100% 100%);
  border-radius: 8px;
  background: linear-gradient(0deg, #f2a0b5, #ffc8d4);
}

.envelope__flap {
  z-index: 4;
  clip-path: polygon(0 0, 50% 56%, 100% 0);
  transform-origin: 50% 0;
  border-radius: 8px;
  background:
    linear-gradient(180deg, rgba(255, 238, 242, 0.68), rgba(255, 184, 200, 0.76)),
    linear-gradient(180deg, #ffb8c8, #ffe2e8);
  transition: transform 600ms cubic-bezier(0.2, 0.85, 0.2, 1);
}

.envelope__back-panel {
  z-index: 1;
  background:
    linear-gradient(90deg, transparent 49.8%, rgba(185, 93, 118, 0.2) 50%, transparent 50.2%),
    linear-gradient(145deg, #ffd8e0, #f4a4b9);
}

.envelope__back-flap {
  z-index: 2;
  clip-path: polygon(0 0, 50% 55%, 100% 0, 100% 100%, 0 100%);
  background:
    linear-gradient(180deg, rgba(255, 234, 239, 0.78), rgba(244, 158, 181, 0.52)),
    linear-gradient(90deg, rgba(185, 93, 118, 0.16), transparent 30%, transparent 70%, rgba(185, 93, 118, 0.16));
}

.envelope:hover .envelope__address,
.envelope:focus-visible .envelope__address {
  transform: translateY(-5px);
}

.envelope-scene.is-flipped .envelope {
  transform: translateY(-4px);
}

.envelope-scene.is-flipped .envelope__face--front {
  opacity: 0;
  transform: rotateY(180deg);
}

.envelope-scene.is-flipped .envelope__face--back {
  opacity: 1;
  transform: rotateY(0deg);
}

.envelope-scene.is-flipped .primary-button {
  background: linear-gradient(135deg, #d66c88, #ba5b75);
  color: #fffdf8;
  box-shadow: 0 14px 32px rgba(185, 93, 118, 0.2);
}

.envelope-scene.is-open .cover-panel {
  pointer-events: none;
  opacity: 0;
  transform: translateY(34px) scale(0.9);
}

.envelope-scene.is-open .envelope__flap {
  transform: rotateX(170deg);
}

.primary-button,
.secondary-button {
  min-height: 44px;
  border: 1px solid rgba(185, 93, 118, 0.24);
  border-radius: 999px;
  background: #fff4f7;
  color: var(--rose-deep);
  cursor: pointer;
  font-weight: 700;
  letter-spacing: 0;
  box-shadow: 0 10px 28px rgba(185, 93, 118, 0.12);
}

.primary-button {
  min-width: 128px;
  padding: 0 30px;
}

.letter {
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 1;
  display: flex;
  flex-direction: column;
  width: min(94vw, 640px);
  min-height: min(620px, 86vh);
  max-height: min(86vh, 760px);
  padding: clamp(28px, 4.5vw, 44px) clamp(24px, 4.8vw, 48px) clamp(24px, 4vw, 36px);
  border: 1px solid rgba(243, 217, 220, 0.92);
  border-radius: 8px;
  background:
    radial-gradient(circle at 14% 10%, rgba(255, 236, 241, 0.9), transparent 12rem),
    radial-gradient(circle at 88% 96%, rgba(246, 225, 230, 0.74), transparent 11rem),
    linear-gradient(rgba(238, 143, 167, 0.075) 1px, transparent 1px) 0 76px / 100% 2.15rem,
    var(--paper);
  box-shadow:
    0 26px 80px rgba(166, 83, 112, 0.18),
    inset 0 1px 0 rgba(255, 255, 255, 0.86);
  opacity: 0;
  overflow: auto;
  overscroll-behavior: contain;
  pointer-events: none;
  transform: translate(-50%, -50%) rotateY(-14deg) translateY(28px) scale(0.92);
  transition:
    opacity 420ms ease 180ms,
    transform 620ms cubic-bezier(0.2, 0.9, 0.2, 1) 160ms;
}

.letter::before {
  position: sticky;
  top: -1px;
  z-index: 4;
  display: block;
  height: 22px;
  margin: calc(clamp(28px, 4.5vw, 44px) * -1) calc(clamp(24px, 4.8vw, 48px) * -1) 0;
  content: "";
  pointer-events: none;
  background: linear-gradient(var(--paper), rgba(255, 253, 248, 0));
}

.letter::-webkit-scrollbar {
  width: 8px;
}

.letter::-webkit-scrollbar-thumb {
  border: 2px solid rgba(255, 253, 248, 0.9);
  border-radius: 999px;
  background: rgba(185, 93, 118, 0.28);
}

.letter::-webkit-scrollbar-track {
  background: transparent;
}

.envelope-scene.is-open .letter {
  z-index: 3;
  opacity: 1;
  pointer-events: auto;
  transform: translate(-50%, -50%) rotateY(0) translateY(0) scale(1);
}

.letter__progress {
  position: sticky;
  top: 0;
  z-index: 5;
  height: 3px;
  margin: -22px calc(clamp(24px, 4.8vw, 48px) * -1) 17px;
  overflow: hidden;
  border-radius: 999px;
  background: rgba(185, 93, 118, 0.08);
}

.letter__progress span {
  display: block;
  width: 100%;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, rgba(233, 148, 169, 0.42), rgba(185, 93, 118, 0.62));
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 120ms linear;
}

.letter__close {
  position: sticky;
  top: 10px;
  z-index: 6;
  align-self: flex-end;
  margin: -16px -12px 0 0;
  box-shadow: 0 10px 24px rgba(185, 93, 118, 0.1);
}

.icon-button {
  display: grid;
  width: 38px;
  height: 38px;
  place-items: center;
  border: 1px solid rgba(201, 95, 125, 0.2);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.9);
  color: var(--rose-deep);
  cursor: pointer;
  font-size: 1.45rem;
  line-height: 1;
}

.letter__kicker {
  margin: 0 0 20px;
  color: var(--rose-deep);
  font-size: clamp(1.08rem, 3.3vw, 1.24rem);
  font-weight: 700;
}

.letter__body {
  display: grid;
  gap: 17px;
  color: #5d4350;
  font-size: clamp(0.98rem, 2.8vw, 1.05rem);
  line-height: 2.02;
  text-wrap: pretty;
}

.letter__body p {
  margin: 0;
  text-indent: 2em;
}

.letter__footer {
  margin-top: 12px;
  padding-top: 26px;
  color: var(--muted);
  text-align: right;
  line-height: 1.8;
}

.letter__footer p {
  margin: 0;
}

.letter__footer time {
  display: block;
  font-size: 0.92rem;
}

.secondary-button {
  width: 100%;
  margin-top: 20px;
  background: rgba(255, 244, 247, 0.76);
  transition:
    background-color 180ms ease,
    color 180ms ease,
    transform 180ms ease,
    box-shadow 180ms ease;
}

.secondary-button:hover {
  background: rgba(255, 230, 237, 0.92);
  box-shadow: 0 14px 30px rgba(185, 93, 118, 0.15);
  transform: translateY(-1px);
}

.secondary-button[hidden],
.envelope__hint[hidden] {
  display: none;
}

@media (max-width: 390px) {
  .page-shell {
    padding: 22px 14px;
  }

  .letter-stage {
    min-height: 560px;
  }

  .envelope-scene {
    min-height: 500px;
  }

  .letter {
    width: min(94vw, 420px);
    min-height: min(640px, 86vh);
    padding: 28px 20px 22px;
  }

  .letter::before {
    margin: -28px -20px 0;
  }

  .letter__progress {
    margin: -22px -20px 15px;
  }

  .letter__body {
    gap: 15px;
    line-height: 1.92;
  }
}

@media (min-width: 760px) {
  .page-shell {
    padding: 40px 24px;
  }

  .letter-stage {
    min-height: 680px;
  }
}

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