styles.css

:root {
  --bg0: #070815;
  --paper: #fff7f0;
  --paper2: #fff0e3;
  --ink: #15121b;
  --env: #f5d6c6;
  --env2: #f0c8b3;
  --env3: #e7b59a;
  --shadow: rgba(0, 0, 0, 0.28);
}

 { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: ui-sans-serif, system-ui, sans-serif;
  color: #eae7ff;
  overflow: hidden;
  background: radial-gradient(1200px 700px at 50% 30%, #1a1e55 0%, var(--bg0) 60%, #050512 100%);
}

.bg {
  position: fixed;
  inset: 0;
  background: radial-gradient(700px 420px at 25% 15%, rgba(255, 77, 141, 0.16), transparent 60%);
  pointer-events: none;
}

.stage {
  height: 100%;
  display: grid;
  place-items: start center;
  padding-top: 24px;
}

.scene {
  width: min(1000px, 96vw);
  height: min(780px, 92vh);
  position: relative;
  display: grid;
  place-items: start center;
  perspective: 1400px;
}

/* Envelope Container */
.envelope-wrap {
  position: relative;
  width: min(520px, 92vw);
  height: 420px;
  display: grid;
  place-items: start center;
  transform-style: preserve-3d;
}

.envelope-wrap.is-falling {
  animation: env-fall 900ms cubic-bezier(.2,.8,.2,1) forwards;
}

@keyframes env-fall {
  0% { transform: translateY(-520px) rotateZ(-4deg) rotateX(18deg); }
  68% { transform: translateY(16px) rotateZ(2deg) rotateX(6deg); }
  100% { transform: translateY(0px) rotateZ(0deg) rotateX(0deg); }
}

/* Shadow */
.shadow {
  position: absolute;
  top: 260px;
  width: 340px;
  height: 60px;
  background: radial-gradient(closest-side, rgba(0, 0, 0, 0.25), transparent 70%);
  transform: translateZ(-1px);
  opacity: 0.18;
  filter: blur(0.5px);
}
.envelope-wrap.is-falling .shadow {
  animation: shadow-in 900ms cubic-bezier(.2,.8,.2,1) forwards;
}
@keyframes shadow-in {
  0% { opacity: 0; transform: translateY(0) scale(0.7); }
  68% { opacity: 0.26; transform: translateY(0) scale(1.05); }
  100% { opacity: 0.18; transform: translateY(0) scale(1); }
}

/* Envelope Parts */
.envelope {
  position: absolute;
  top: 40px;
  width: min(460px, 88vw);
  height: 280px;
  z-index: 2;
  transform-style: preserve-3d;
  filter: drop-shadow(0 20px 30px rgba(0, 0, 0, 0.35));
}

.env-back {
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, var(--env) 0%, var(--env2) 100%);
  border-radius: 18px;
}

.env-front {
  position: absolute;
  inset: 0;
  border-radius: 18px;
  background: var(--env2);
  clip-path: polygon(0% 0%, 100% 0%, 100% 100%, 50% 64%, 0% 100%);
}

.env-letter-slot {
  position: absolute;
  left: 24px; right: 24px; top: 26px; height: 78px;
  border-radius: 14px;
  background: rgba(0,0,0,0.05);
}

.env-flap {
  position: absolute;
  inset: 0;
  border-radius: 18px;
  transform-origin: 50% 0%;
  background: var(--env3);
  clip-path: polygon(0% 0%, 100% 0%, 50% 58%);
  transition: transform 650ms cubic-bezier(.2,.8,.2,1);
  transform-style: preserve-3d;
}
.envelope-wrap.is-open .env-flap {
  transform: rotateX(165deg);
}

/* Paper / Letter */
.paper {
  position: absolute;
  top: 78px;
  width: min(520px, 92vw);
  height: min(650px, 82vh);
  z-index: 5;
  transform-style: preserve-3d;
  transform: translateY(120px) scale(0.96);
  opacity: 0;
  pointer-events: none;
  transition: transform 850ms cubic-bezier(.16,.85,.2,1), opacity 350ms ease;
}
.paper.is-hidden { display: none; }

.envelope-wrap.is-paper-out .paper {
  display: block;
  opacity: 1;
  transform: translateY(0px) scale(1);
  pointer-events: auto;
}

.paper-inner {
  position: absolute;
  inset: 0;
  border-radius: 18px;
  transform-style: preserve-3d;
}

.paper-face {
  position: absolute;
  inset: 0;
  background: radial-gradient(1200px 900px at 40% 0%, var(--paper) 0%, var(--paper2) 56%, #ffe9d7 100%);
  border-radius: 18px;
  color: var(--ink);
  box-shadow: 0 18px 40px var(--shadow);
  padding: 40px;
  overflow-y: auto;
}

/* Letter Content Typography */
.letter-content {
  font-size: 18px;
  line-height: 1.6;
}
.letter-content h1 {
  margin-top: 0;
  font-size: 24px;
  color: rgba(21, 18, 27, 0.85);
}
.letter-content p {
  margin-bottom: 1.5em;
  color: rgba(21, 18, 27, 0.75);
}
.letter-content .sign {
  margin-top: 40px;
  font-weight: bold;
  font-style: italic;
}