/* ---------------------------------------------------------------
   一封未拆的信 — envelope / folded letter
   Palette and type are drawn from the object itself: kraft paper,
   oxblood wax, a dim desk, and ink.
   --------------------------------------------------------------- */

:root {
  --desk-deep: #0d0a07;
  --desk: #17110b;
  --desk-warm: #2b2116;
  --paper: #cbaa7c;
  --paper-lit: #dcc094;
  --ink: #382a1c;
  --ink-soft: #6b5640;
  --wax: #7d2b26;
  --warm-white: #f0dcc0;

  --serif: "Noto Serif CJK SC", "Noto Serif SC", "Songti SC", "STSong",
    "Source Han Serif SC", "SimSun", Georgia, serif;
  --sans: ui-sans-serif, -apple-system, "PingFang SC", "Noto Sans CJK SC",
    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;

  --sheet-w: min(560px, 54vw, 56vh);
  --sheet-h: calc(var(--sheet-w) * 1.4142);
  --env-w: min(calc(var(--sheet-w) * 1.16), 92vw);
  --env-h: calc(var(--env-w) * 0.655);

  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-fold: cubic-bezier(0.6, 0, 0.3, 1);
  --ease-soft: cubic-bezier(0.33, 1, 0.68, 1);
}

* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
}

body {
  margin: 0;
  background: var(--desk-deep);
  color: var(--warm-white);
  font-family: var(--serif);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow: hidden;
}

::selection {
  background: rgba(125, 43, 38, 0.3);
  color: #241a10;
}

button {
  font: inherit;
  color: inherit;
}

:focus-visible {
  outline: 2px solid rgba(240, 220, 190, 0.55);
  outline-offset: 7px;
  border-radius: 2px;
}

/* ---------- scene ---------- */

.scene {
  position: fixed;
  inset: 0;
  min-height: 100svh;
  overflow: hidden;
  isolation: isolate;
}

.backdrop {
  position: absolute;
  inset: 0;
  background:
    radial-gradient(58% 44% at 50% 40%, rgba(190, 140, 86, 0.14), transparent 68%),
    radial-gradient(120% 90% at 50% 18%, #2e2418 0%, #1a130d 44%, #0d0a07 100%);
}

.backdrop::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(
    42% 34% at 50% 42%,
    rgba(233, 186, 126, 0.11),
    transparent 72%
  );
  animation: breathe 13s ease-in-out infinite;
}

.backdrop::after {
  content: "";
  position: absolute;
  inset: 0;
  background-image: url("/assets/grain.png");
  background-size: 96px 96px;
  opacity: 0.5;
  mix-blend-mode: overlay;
  pointer-events: none;
}

@keyframes breathe {
  0%,
  100% {
    opacity: 0.75;
    transform: scale(1);
  }
  50% {
    opacity: 1;
    transform: scale(1.04);
  }
}

.dust {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  opacity: 0.55;
}

.stage {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
}

/* ---------- envelope ---------- */

.envelope {
  position: relative;
  z-index: 2;
  width: var(--env-w);
  height: var(--env-h);
  padding: 0;
  border: 0;
  background: none;
  cursor: pointer;
  perspective: 1500px;
  -webkit-tap-highlight-color: transparent;
  transition:
    transform 1.15s var(--ease-out) 0.95s,
    opacity 0.6s var(--ease-soft) 1.02s;
}

.envelope:hover .env-float {
  transform: translateY(-5px);
}

.envelope:active .env-float {
  transform: translateY(-1px) scale(0.997);
}

.env-float {
  position: absolute;
  inset: 0;
  display: block;
  transition: transform 0.7s var(--ease-out);
}

.env-body {
  position: absolute;
  inset: 0;
  display: block;
  border-radius: 2px;
  background-color: #c6a476;
  background-image:
    linear-gradient(155deg, rgba(255, 242, 220, 0.1), transparent 40%),
    url("/assets/kraft.jpg");
  background-position: center;
  background-size: cover;
  background-repeat: no-repeat;
  box-shadow:
    0 42px 66px -26px rgba(0, 0, 0, 0.9),
    0 14px 26px -12px rgba(0, 0, 0, 0.6);
}

.env-body::before {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: linear-gradient(
    160deg,
    rgba(255, 246, 228, 0.14),
    transparent 34%,
    rgba(56, 35, 16, 0.12) 100%
  );
  box-shadow:
    inset 0 0 0 1px rgba(92, 62, 32, 0.25),
    inset 0 0 46px rgba(0, 0, 0, 0.16);
}

.env-mouth {
  position: absolute;
  top: 0;
  left: 1px;
  right: 1px;
  height: 21%;
  border-radius: 2px 2px 0 0;
  background:
    radial-gradient(88% 76% at 50% 0%, rgba(24, 13, 5, 0.5), transparent 72%),
    linear-gradient(
      to bottom,
      rgba(30, 17, 7, 0.72),
      rgba(30, 17, 7, 0.22) 46%,
      transparent
    );
  opacity: 0;
  transition: opacity 0.6s var(--ease-soft) 0.3s;
}

.env-lining {
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: radial-gradient(
    120% 70% at 50% 0%,
    rgba(38, 22, 9, 0.34),
    transparent 62%
  );
  opacity: 0;
  transition: opacity 0.7s var(--ease-soft) 0.35s;
}

/* the triangular back flap */
.env-flap {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 66%;
  z-index: 3;
  display: block;
  clip-path: polygon(0 0, 100% 0, 50% 100%);
  background-color: #c6a476;
  background-image:
    linear-gradient(178deg, rgba(255, 244, 224, 0.08), transparent 42%),
    url("/assets/kraft.jpg");
  background-position: center top;
  background-size: 100% 152%;
  background-repeat: no-repeat;
  transform-origin: 50% 0;
  transition:
    transform 1.05s var(--ease-fold) 0.3s,
    opacity 0.45s var(--ease-soft) 0.95s;
  filter: drop-shadow(0 1px 0 rgba(255, 246, 228, 0.12))
    drop-shadow(0 10px 14px rgba(0, 0, 0, 0.18));
}

.env-flap-shade {
  position: absolute;
  inset: 0;
  background:
    linear-gradient(180deg, rgba(255, 245, 226, 0.16), transparent 26%),
    radial-gradient(90% 70% at 50% 100%, rgba(61, 38, 15, 0.18), transparent 60%);
}

.env-cast {
  position: absolute;
  left: 50%;
  bottom: -7%;
  width: 88%;
  height: 12%;
  transform: translateX(-50%);
  border-radius: 50%;
  background: rgba(0, 0, 0, 0.55);
  filter: blur(22px);
  z-index: -1;
}

/* wax seal */
.env-seal {
  position: absolute;
  left: 50%;
  top: 59%;
  z-index: 5;
  width: 23.5%;
  aspect-ratio: 1;
  transform: translate(-50%, -50%);
  filter: drop-shadow(0 7px 9px rgba(0, 0, 0, 0.5))
    drop-shadow(0 1px 0 rgba(255, 210, 190, 0.1));
  transition: transform 0.5s var(--ease-out);
}

.envelope:hover .env-seal {
  transform: translate(-50%, -50%) scale(1.035) rotate(-1.5deg);
}

.seal-half {
  position: absolute;
  inset: 0;
  display: block;
  transition:
    transform 0.5s cubic-bezier(0.32, 0.82, 0.4, 1) 0.02s,
    opacity 0.14s ease-out 0.34s;
}

.seal-half svg {
  display: block;
  width: 100%;
  height: 100%;
}

.seal-left {
  clip-path: polygon(
    0 0,
    55% 0,
    48% 16%,
    56% 33%,
    47% 50%,
    55% 68%,
    49% 86%,
    56% 100%,
    0 100%
  );
}

.seal-right {
  clip-path: polygon(
    55% 0,
    100% 0,
    100% 100%,
    56% 100%,
    49% 86%,
    55% 68%,
    47% 50%,
    56% 33%,
    48% 16%
  );
}

/* ---------- states: opened ---------- */

.scene[data-state="opened"] .envelope,
.scene[data-state="unfolded"] .envelope {
  transform: translateY(26vh) scale(0.4) rotate(-2deg);
  opacity: 0;
  pointer-events: none;
}

.scene[data-state="opened"] .env-flap,
.scene[data-state="unfolded"] .env-flap {
  transform: rotateX(175deg);
  opacity: 0;
}

.scene[data-state="opened"] .env-mouth,
.scene[data-state="unfolded"] .env-mouth,
.scene[data-state="opened"] .env-lining,
.scene[data-state="unfolded"] .env-lining {
  opacity: 1;
}

.scene[data-state="opened"] .seal-left,
.scene[data-state="unfolded"] .seal-left {
  transform: translate(-13%, 26%) rotate(-9deg) scale(0.98);
  opacity: 0;
}

.scene[data-state="opened"] .seal-right,
.scene[data-state="unfolded"] .seal-right {
  transform: translate(14%, 24%) rotate(8deg) scale(0.98);
  opacity: 0;
}

/* ---------- letter ---------- */

.letter {
  position: absolute;
  left: 50%;
  top: 50%;
  z-index: 5;
  width: var(--sheet-w);
  height: var(--sheet-h);
  transform: translate(-50%, -50%) translateY(7%) scale(0.955) rotate(-0.8deg);
  opacity: 0;
  pointer-events: none;
  perspective: 2100px;
  perspective-origin: 50% 50%;
  transition:
    transform 1.05s var(--ease-out) 0.85s,
    opacity 0.7s var(--ease-soft) 0.85s;
}

.scene[data-state="opened"] .letter {
  transform: translate(-50%, -50%) rotate(-0.55deg);
  opacity: 1;
}

.scene[data-state="closed"] .letter {
  transform: translate(-50%, -50%) translateY(7%) scale(0.955) rotate(-0.8deg);
}

.scene[data-state="unfolded"] .letter {
  transform: translate(-50%, -50%);
  opacity: 1;
}

.scene[data-state="opened"] .letter {
  pointer-events: none;
  cursor: pointer;
}

.scene[data-state="opened"] .panel {
  pointer-events: auto;
  cursor: pointer;
}

.sheet {
  position: absolute;
  inset: 0;
  transform-style: preserve-3d;
}

.panel {
  position: absolute;
  left: 0;
  right: 0;
  height: 33.3334%;
  background-color: #c6a476;
  background-image: url("/assets/kraft.jpg");
  background-repeat: no-repeat;
  background-size: 100% 300%;
  backface-visibility: visible;
  will-change: transform;
  box-shadow: 0 1px 0 rgba(255, 244, 224, 0.16);
  transition: transform 1.02s var(--ease-fold) 0.08s;
}

.panel-top {
  top: 0;
  background-position: 50% 0;
  transform-origin: 50% 100%;
  z-index: 4;
}

.panel-mid {
  top: 33.3333%;
  background-position: 50% 50%;
  z-index: 1;
  box-shadow: none;
}

.panel-bot {
  top: 66.6666%;
  background-position: 50% 100%;
  transform-origin: 50% 0;
  z-index: 3;
  transition-delay: 0.14s;
}

.scene[data-state="closed"] .panel-top,
.scene[data-state="opened"] .panel-top {
  transform: translateZ(7px) rotateX(180deg);
  box-shadow:
    0 9px 20px rgba(0, 0, 0, 0.34),
    0 1px 0 rgba(255, 244, 224, 0.16);
}

.scene[data-state="closed"] .panel-bot,
.scene[data-state="opened"] .panel-bot {
  transform: translateZ(3px) rotateX(-180deg);
  box-shadow:
    0 5px 14px rgba(0, 0, 0, 0.28),
    0 1px 0 rgba(255, 244, 224, 0.13);
}

.scene[data-state="unfolded"] .panel {
  box-shadow: none;
}

.scene[data-state="closed"] .letter-content,
.scene[data-state="opened"] .letter-content {
  opacity: 0;
  pointer-events: none;
}

.sheet-paper {
  position: absolute;
  inset: 0;
  z-index: 4;
  pointer-events: none;
  background-color: #c6a476;
  background-image: none;
  opacity: 0;
  transition: opacity 0.18s ease-out 0s;
}

.scene[data-state="unfolded"] .sheet-paper {
  background: url("/assets/kraft.jpg") center / 100% 100% no-repeat;
  opacity: 1;
  transition: opacity 0.32s ease-out 0.95s;
}

.sheet-edge {
  position: absolute;
  inset: 0;
  z-index: 7;
  pointer-events: none;
  background: linear-gradient(
    158deg,
    rgba(255, 250, 236, 0.06),
    transparent 42%,
    rgba(78, 51, 24, 0.06)
  );
  box-shadow:
    inset 0 0 0 1px rgba(255, 246, 228, 0.14),
    inset 0 0 56px rgba(0, 0, 0, 0.1),
    0 36px 70px -18px rgba(0, 0, 0, 0.62);
  opacity: 0;
  transition: opacity 0.22s ease-out 0s;
}

.scene[data-state="unfolded"] .sheet-edge {
  opacity: 1;
  transition: opacity 0.45s var(--ease-soft) 0.82s;
}

.crease {
  position: absolute;
  left: 0;
  right: 0;
  height: 2px;
  margin-top: -1px;
  z-index: 5;
  pointer-events: none;
  transform: translateZ(15px);
  background: linear-gradient(
    to bottom,
    rgba(74, 48, 22, 0.2) 0,
    rgba(74, 48, 22, 0.2) 1px,
    rgba(255, 248, 232, 0.16) 1px,
    rgba(255, 248, 232, 0.16) 2px
  );
  opacity: 0.7;
  transition: opacity 0.4s;
}

.crease-a {
  top: 33.3333%;
}

.crease-b {
  top: 66.6666%;
}

.scene[data-state="unfolded"] .crease {
  opacity: 0.7;
}

.letter::before {
  content: "";
  position: absolute;
  left: 4%;
  right: 4%;
  top: 33.6%;
  height: 32.8%;
  z-index: -1;
  border-radius: 4px;
  background: rgba(0, 0, 0, 0.78);
  filter: blur(26px);
  transform: translateY(13px);
  transition: opacity 0.5s var(--ease-soft);
}

.letter::after {
  content: "";
  position: absolute;
  inset: 33.3333% 0;
  z-index: 5;
  pointer-events: none;
  box-shadow:
    inset 0 1px 0 rgba(255, 249, 235, 0.16),
    inset 0 -2px 6px rgba(60, 39, 17, 0.12);
  opacity: 1;
  transition: opacity 0.4s;
}

.scene[data-state="unfolded"] .letter::before,
.scene[data-state="unfolded"] .letter::after {
  opacity: 0;
}

.thread {
  position: absolute;
  top: 33.3333%;
  left: -1px;
  right: -1px;
  height: 33.3334%;
  z-index: 8;
  pointer-events: none;
  transform: translateZ(16px);
  filter: drop-shadow(0 1px 1.5px rgba(0, 0, 0, 0.45));
  opacity: 0;
  transition: opacity 0.2s ease-out 0s;
}

.thread svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
  overflow: visible;
}

.knot {
  position: absolute;
  left: 50%;
  top: 53.4%;
  width: 10px;
  height: 8px;
  transform: translate(-50%, -50%) rotate(-8deg);
  border: 1.5px solid #6a382a;
  border-radius: 50%;
  box-shadow: 0 1px 1px rgba(0, 0, 0, 0.25);
}

.knot::before,
.knot::after {
  content: "";
  position: absolute;
  top: 7px;
  width: 1.5px;
  height: 8px;
  background: #6a382a;
  border-radius: 1px;
}

.knot::before {
  left: 2px;
  transform: rotate(18deg);
  transform-origin: top center;
}

.knot::after {
  right: 2px;
  transform: rotate(-16deg);
  transform-origin: top center;
}

.scene[data-state="opened"] .thread {
  opacity: 1;
  transition: opacity 0.32s ease-out 1.05s;
}

.stack-edge {
  position: absolute;
  left: 1px;
  right: 1px;
  top: 66.45%;
  height: 4px;
  z-index: 9;
  pointer-events: none;
  transform: translateZ(16px);
  border-radius: 0 0 2px 2px;
  background: linear-gradient(
    to bottom,
    rgba(255, 248, 232, 0.22) 0,
    rgba(150, 118, 80, 0.5) 1px,
    rgba(112, 84, 53, 0.55) 2px,
    rgba(74, 50, 26, 0.4) 3px,
    transparent 4px
  );
  box-shadow: 0 3px 5px rgba(0, 0, 0, 0.22);
  opacity: 0;
  transition: opacity 0.2s ease-out 0s;
}

.scene[data-state="opened"] .stack-edge {
  opacity: 1;
  transition-delay: 1.05s;
}

.focus-ring {
  position: absolute;
  left: 1px;
  right: 1px;
  top: 33.3333%;
  height: 33.3334%;
  z-index: 9;
  border: 2px solid rgba(240, 220, 190, 0.5);
  border-radius: 2px;
  opacity: 0;
  pointer-events: none;
}

.letter:focus-visible .focus-ring {
  opacity: 1;
}

.letter-content {
  position: absolute;
  inset: 0;
  z-index: 6;
  display: flex;
  flex-direction: column;
  padding: calc(var(--sheet-w) * 0.085) calc(var(--sheet-w) * 0.092)
    calc(var(--sheet-w) * 0.075);
  overflow-y: auto;
  overscroll-behavior: contain;
  color: var(--ink);
  font-size: clamp(15px, calc(var(--sheet-w) * 0.0357), 19px);
  line-height: 2.04;
  letter-spacing: 0.018em;
  opacity: 0;
  transform: translateY(4px);
  cursor: default;
  transition:
    opacity 0.24s ease-out 0s,
    transform 0.3s ease-out 0s;
  scrollbar-width: thin;
  scrollbar-color: rgba(82, 58, 34, 0.32) transparent;
}

.scene[data-state="unfolded"] .letter-content {
  opacity: 1;
  transform: none;
  pointer-events: auto;
  user-select: text;
  -webkit-user-select: text;
  transition:
    opacity 0.45s var(--ease-soft) 0.98s,
    transform 0.6s var(--ease-out) 0.98s;
}

.letter-content::-webkit-scrollbar {
  width: 6px;
}

.letter-content::-webkit-scrollbar-thumb {
  background: rgba(82, 58, 34, 0.3);
  border-radius: 3px;
}

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

.letter-content.is-scrollable {
  -webkit-mask-image: linear-gradient(
    to bottom,
    #000 0,
    #000 calc(100% - 54px),
    transparent 100%
  );
  mask-image: linear-gradient(
    to bottom,
    #000 0,
    #000 calc(100% - 54px),
    transparent 100%
  );
}

.letter-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 1.2em;
  margin-bottom: 2.7em;
  font-family: var(--sans);
  font-size: 0.63em;
  font-weight: 500;
  letter-spacing: 0.18em;
  color: rgba(56, 40, 24, 0.86);
}

.letter-place {
  padding-left: 0.06em;
}

.letter-date {
  font-variant-numeric: tabular-nums;
}

.salutation {
  margin: 0 0 1.35em;
  letter-spacing: 0.12em;
  font-size: 1.02em;
}

.letter-content p {
  margin: 0 0 0.9em;
  text-indent: 2em;
  text-align: justify;
  text-justify: inter-ideograph;
  color: #3b2c1d;
}

.signature {
  margin-top: 2.35em;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 0.55em;
  color: rgba(52, 37, 21, 0.82);
}

.sign-name {
  font-size: 1.16em;
  letter-spacing: 0.24em;
  padding-right: 0.06em;
}

.sign-date {
  font-size: 0.74em;
  letter-spacing: 0.14em;
  color: rgba(56, 40, 24, 0.86);
}

/* ---------- hint / fold ---------- */

.hint {
  position: absolute;
  left: 50%;
  bottom: clamp(26px, 5.6vh, 60px);
  margin: 0;
  transform: translateX(-50%);
  font-family: var(--sans);
  font-size: 11.5px;
  font-weight: 400;
  letter-spacing: 0.34em;
  text-indent: 0.34em;
  color: rgba(240, 222, 196, 0.64);
  white-space: nowrap;
  pointer-events: none;
  transition:
    bottom 0.75s var(--ease-out),
    opacity 0.5s var(--ease-soft),
    transform 0.5s var(--ease-out);
}

.scene[data-state="opened"] .hint,
.scene[data-state="unfolded"] .hint {
  bottom: calc(50% - var(--sheet-h) / 6 - 58px);
}

.hint.is-out {
  opacity: 0;
  transform: translate(-50%, 6px);
}

.scene[data-state="unfolded"] .hint {
  opacity: 0;
  transform: translate(-50%, 8px);
}

.fold {
  position: absolute;
  right: clamp(20px, 3.2vw, 46px);
  bottom: clamp(22px, 4.4vh, 44px);
  z-index: 10;
  padding: 8px 2px;
  border: 0;
  background: none;
  font-family: var(--sans);
  font-size: 11px;
  letter-spacing: 0.26em;
  text-indent: 0.26em;
  color: rgba(240, 222, 196, 0.56);
  cursor: pointer;
  opacity: 0;
  transform: translateY(6px);
  pointer-events: none;
  transition:
    opacity 0.5s var(--ease-soft) 0.85s,
    transform 0.5s var(--ease-out) 0.85s,
    color 0.3s;
}

.scene[data-state="unfolded"] .fold {
  opacity: 1;
  transform: none;
  pointer-events: auto;
}

.fold:hover {
  color: rgba(240, 220, 190, 0.8);
}

/* ---------- responsive ---------- */

@media (max-width: 720px) {
  :root {
    --sheet-w: min(92vw, 62vh);
    --env-w: min(92vw, calc(var(--sheet-w) * 1.12));
    --env-h: calc(var(--env-w) * 0.64);
  }

  .scene[data-state="opened"] .envelope,
  .scene[data-state="unfolded"] .envelope {
    transform: translateY(24vh) scale(0.5);
  }

  .letter {
    transform: translate(-50%, -50%) translateY(6%) scale(0.97) rotate(-0.5deg);
  }

  .letter-head {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.5em;
    margin-bottom: 2.2em;
  }

  .signature {
    margin-top: 1.8em;
  }

  .hint {
    letter-spacing: 0.26em;
    text-indent: 0.26em;
  }
}

@media (max-height: 620px) and (min-width: 721px) {
  :root {
    --sheet-w: min(56vw, 54vh);
  }

  .letter-content {
    font-size: clamp(13px, calc(var(--sheet-w) * 0.033), 16px);
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    transition-delay: 0ms !important;
  }

  .dust {
    display: none;
  }
}

/* hide the sprite */
.svg-defs {
  position: absolute;
  width: 0;
  height: 0;
  overflow: hidden;
}

/* used by the instant deep-link / capture path */
html.instant *,
html.instant *::before,
html.instant *::after {
  transition: none !important;
  animation: none !important;
}