@font-face {
  font-family: "Jinghua Laosong";
  src: url("./assets/fonts/jinghua-laosong.ttf") format("truetype");
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}

:root {
  --ink: #201b14;
  --paper-texture: url("./assets/intro-page/envelope-yellow-texture-clean.jpg");
  --cover-bg: url("./assets/intro-page/jellyfish-bg.png");
}

* {
  box-sizing: border-box;
}

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

body {
  position: relative;
  overflow-x: hidden;
  background: #050505;
  color: var(--ink);
  font-family: "Jinghua Laosong", "Songti SC", "SimSun", serif;
}

.page-background {
  position: fixed;
  inset: 0;
  z-index: 0;
  width: 100vw;
  height: 100vh;
  object-fit: cover;
  object-position: center;
  pointer-events: none;
  user-select: none;
  animation: jellyfish-drift 22s ease-in-out infinite alternate;
  transform: scale(1.04);
  transform-origin: 50% 45%;
}

body::before {
  position: fixed;
  inset: -4vh -4vw;
  z-index: 0;
  content: "";
  pointer-events: none;
  background: var(--cover-bg) center / cover no-repeat;
  filter: blur(8px) brightness(1.08);
  mix-blend-mode: screen;
  opacity: 0.22;
  animation: jellyfish-depth 28s ease-in-out infinite alternate;
  transform: scale(1.12) translate3d(-1.2rem, 0.6rem, 0);
}

body::after {
  position: fixed;
  inset: 0;
  z-index: 0;
  content: "";
  pointer-events: none;
  background: linear-gradient(180deg, rgba(0, 0, 0, 0.03), rgba(0, 0, 0, 0.18));
}

.intro-page {
  position: relative;
  z-index: 1;
  min-height: 100svh;
  display: grid;
  place-items: center;
  padding: clamp(1.2rem, 4vw, 4rem);
}

.envelope-stage {
  width: min(100%, 62rem);
  min-height: calc(100svh - clamp(2.4rem, 8vw, 8rem));
  display: grid;
  place-items: center;
}

.interactive-envelope {
  position: relative;
  width: clamp(19rem, 46vw, 35rem);
  aspect-ratio: 1.18;
  cursor: pointer;
  outline: none;
  filter:
    drop-shadow(0 1.6rem 2rem rgba(0, 0, 0, 0.58))
    drop-shadow(0 0.25rem 0.18rem rgba(255, 255, 255, 0.06));
  transform-style: preserve-3d;
}

.interactive-envelope:focus-visible {
  outline: 2px solid rgba(242, 232, 196, 0.76);
  outline-offset: 0.8rem;
}

.interactive-envelope.is-open {
  filter: none;
  transform-style: flat;
}

.envelope-flap {
  position: absolute;
  left: 10%;
  right: 10%;
  top: -8%;
  height: 54%;
  z-index: 1;
  background:
    linear-gradient(105deg, rgba(79, 67, 38, 0.16), transparent 18%, transparent 82%, rgba(255, 255, 238, 0.18)),
    radial-gradient(ellipse at 50% 18%, rgba(255, 255, 242, 0.38), transparent 56%),
    var(--paper-texture);
  background-size: auto, auto, cover;
  background-position: center;
  border: 1px solid rgba(217, 205, 164, 0.72);
  border-radius: 1.2rem 1.2rem 0.2rem 0.2rem;
  clip-path: polygon(50% 0, 100% 84%, 80% 100%, 20% 100%, 0 84%);
  box-shadow:
    inset 0 0.18rem 0.28rem rgba(255, 255, 244, 0.5),
    inset 0 -1rem 1.4rem rgba(91, 78, 45, 0.17),
    0 0.7rem 0.9rem rgba(0, 0, 0, 0.18);
  opacity: 0.96;
  transform: rotateX(18deg) translateY(0.25rem);
  transform-origin: center bottom;
}

.letter-sheet {
  position: absolute;
  left: 50%;
  top: 18%;
  z-index: 2;
  width: 62%;
  height: 62%;
  overflow: hidden;
  padding: 0.52rem;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.7), rgba(246, 240, 218, 0.22)),
    var(--paper-texture);
  background-size: auto, cover;
  background-position: center;
  border: 1px solid rgba(235, 226, 190, 0.95);
  box-shadow:
    0 0.45rem 0.8rem rgba(0, 0, 0, 0.2),
    inset 0 0 0 1px rgba(255, 255, 246, 0.65);
  transform: translateX(-50%);
  transform-origin: center bottom;
  transition:
    top 620ms cubic-bezier(0.2, 0.82, 0.2, 1),
    width 620ms cubic-bezier(0.2, 0.82, 0.2, 1),
    height 620ms cubic-bezier(0.2, 0.82, 0.2, 1),
    padding 620ms cubic-bezier(0.2, 0.82, 0.2, 1),
    transform 620ms cubic-bezier(0.2, 0.82, 0.2, 1);
}

.interactive-envelope:hover .letter-sheet {
  top: -5%;
  width: 66%;
  height: 86%;
  transform: translateX(-50%) rotate(-0.4deg);
}

.interactive-envelope.is-open .letter-sheet {
  position: fixed;
  top: 50%;
  left: 50%;
  z-index: 50;
  width: min(42rem, 88vw);
  height: min(39rem, 84svh);
  overflow: auto;
  padding: clamp(0.8rem, 2vw, 1.2rem);
  transform: translate(-50%, -50%);
}

.portrait-panel {
  width: 100%;
  height: clamp(9.5rem, 19vw, 16rem);
  margin: 0 0 1rem;
  overflow: hidden;
  background: #0e0e0e;
  border: 1px solid rgba(248, 240, 207, 0.78);
}

.portrait-panel img {
  width: 100%;
  height: 100%;
  display: block;
  object-fit: cover;
  object-position: 50% 50%;
  filter: grayscale(1) contrast(1.05) sepia(0.16);
}

.intro-copy {
  color: var(--ink);
  opacity: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  transition: opacity 360ms ease;
}

.interactive-envelope:hover .intro-copy {
  opacity: 0.42;
}

.interactive-envelope.is-open .intro-copy {
  opacity: 1;
}

.intro-line {
  margin: 0;
  width: min(100%, 34rem);
  font-size: clamp(0.82rem, 1.1vw, 1rem);
  line-height: 1.9;
  letter-spacing: 0;
}

.intro-copy .intro-line:nth-of-type(7) {
  width: 100%;
  max-width: none;
  white-space: nowrap;
  font-size: clamp(0.82rem, 1.1vw, 1rem);
}

.intro-greeting {
  margin-bottom: 0.72rem;
  font-size: clamp(1rem, 1.35vw, 1.22rem);
}

.intro-block,
.intro-closing {
  margin-top: 0.9rem;
}

.envelope-pocket {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 61%;
  z-index: 10;
  overflow: hidden;
  background:
    linear-gradient(90deg, rgba(84, 70, 38, 0.1), transparent 14%, transparent 86%, rgba(255, 255, 236, 0.2)),
    radial-gradient(ellipse at 52% 18%, rgba(255, 255, 238, 0.44), transparent 58%),
    var(--paper-texture);
  background-size: auto, auto, cover;
  background-position: center;
  border: 1px solid rgba(219, 208, 169, 0.88);
  box-shadow:
    inset 0 0 0 1px rgba(255, 255, 242, 0.58),
    inset 0 0.85rem 1rem rgba(255, 255, 238, 0.22),
    inset 0 -1.2rem 1.6rem rgba(110, 94, 56, 0.15);
}

.envelope-pocket::before {
  position: absolute;
  inset: 0;
  z-index: 1;
  content: "";
  background:
    radial-gradient(ellipse at 50% 64%, rgba(91, 79, 49, 0.1), transparent 38%),
    linear-gradient(137deg, transparent 0 49.4%, rgba(102, 89, 55, 0.22) 49.8%, transparent 50.4%),
    linear-gradient(43deg, transparent 0 49.4%, rgba(102, 89, 55, 0.17) 49.8%, transparent 50.4%);
}

.envelope-pocket::after {
  position: absolute;
  left: 18%;
  right: 18%;
  top: -1px;
  height: 48%;
  z-index: 2;
  content: "";
  background:
    linear-gradient(180deg, rgba(255, 252, 226, 0.44), rgba(191, 177, 128, 0.16)),
    var(--paper-texture);
  background-size: auto, cover;
  background-position: center;
  clip-path: polygon(0 0, 100% 0, 50% 100%);
  box-shadow:
    inset 0 0.2rem 0.2rem rgba(255, 255, 236, 0.3),
    inset 0 -0.5rem 0.8rem rgba(91, 76, 44, 0.12);
}

.pocket-fold {
  position: absolute;
  z-index: 3;
  pointer-events: none;
}

.pocket-fold-left,
.pocket-fold-right {
  top: 0;
  bottom: 0;
  width: 31%;
  background:
    linear-gradient(180deg, rgba(255, 254, 230, 0.4), rgba(198, 184, 134, 0.12)),
    var(--paper-texture);
  background-size: auto, cover;
  background-position: center;
  opacity: 0.86;
}

.pocket-fold-left {
  left: 0;
  clip-path: polygon(0 0, 100% 38%, 100% 100%, 0 100%);
}

.pocket-fold-right {
  right: 0;
  clip-path: polygon(100% 0, 0 38%, 0 100%, 100% 100%);
}

.pocket-fold-bottom {
  left: 0;
  right: 0;
  bottom: 0;
  height: 54%;
  background:
    linear-gradient(180deg, rgba(255, 255, 238, 0.12), rgba(194, 179, 127, 0.13)),
    var(--paper-texture);
  background-size: auto, cover;
  background-position: center;
  clip-path: polygon(0 100%, 50% 0, 100% 100%);
  opacity: 0.82;
}

.envelope-label {
  position: absolute;
  left: 50%;
  bottom: 16%;
  z-index: 4;
  display: grid;
  gap: 0.25rem;
  color: rgba(77, 68, 49, 0.5);
  font-size: clamp(0.85rem, 1.5vw, 1.2rem);
  line-height: 1.35;
  letter-spacing: 0.12em;
  text-align: center;
  text-shadow:
    0 1px 0 rgba(255, 255, 238, 0.38),
    0 -1px 0 rgba(77, 68, 49, 0.1);
  transform: translateX(-50%);
  white-space: nowrap;
}

.envelope-label::before {
  display: none;
}

.interactive-envelope.is-open .envelope-pocket,
.interactive-envelope.is-open .envelope-flap {
  opacity: 0.22;
  transition: opacity 360ms ease;
}

@media (max-width: 820px) {
  .intro-page {
    padding: 1.2rem;
  }

  .interactive-envelope {
    width: min(23rem, 88vw);
  }

  .interactive-envelope:hover .letter-sheet {
    top: -4%;
    height: 82%;
  }

  .interactive-envelope.is-open .letter-sheet {
    width: min(22rem, 90vw);
    height: min(34rem, 78svh);
  }

  .portrait-panel {
    height: 12.2rem;
  }

  .intro-copy .intro-line:nth-of-type(7) {
    font-size: clamp(0.82rem, 1.1vw, 1rem);
  }
}

@keyframes jellyfish-drift {
  0% {
    transform: scale(1.04) translate3d(-0.8rem, -0.4rem, 0);
    object-position: 48% 47%;
  }

  50% {
    transform: scale(1.08) translate3d(0.6rem, 0.8rem, 0);
    object-position: 52% 44%;
  }

  100% {
    transform: scale(1.06) translate3d(1rem, -0.2rem, 0);
    object-position: 50% 48%;
  }
}

@keyframes jellyfish-depth {
  0% {
    opacity: 0.16;
    transform: scale(1.12) translate3d(-1.4rem, 0.6rem, 0);
  }

  100% {
    opacity: 0.28;
    transform: scale(1.18) translate3d(1.2rem, -0.8rem, 0);
  }
}