*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  height: 100vh;
  overflow: hidden;
  background-color: #0a0a0a;
  background-image:
    radial-gradient(circle, rgba(255, 255, 255, 0.04) 1px, transparent 1px);
  background-size: 4px 4px;
  -webkit-font-smoothing: antialiased;
}

body::before {
  content: '';
  position: fixed;
  inset: 0;
  background:
    radial-gradient(ellipse at 30% 20%, rgba(255, 255, 255, 0.015) 0%, transparent 60%),
    radial-gradient(ellipse at 70% 80%, rgba(255, 255, 255, 0.01) 0%, transparent 50%);
  pointer-events: none;
}

/* ── Scene ── */

.scene {
  height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2rem;
  perspective: 1200px;
}

/* ── Letter wrapper (preserves 3D) ── */

.letter-wrapper {
  transform-style: preserve-3d;
}

.letter {
  position: relative;
  width: min(88vw, 560px);
  height: min(82vh, 720px);
  transform-style: preserve-3d;
  transition: transform 1s cubic-bezier(0.4, 0.0, 0.2, 1);
  transform: rotate(-1.2deg);
}

.letter.flipped {
  transform: rotate(-1.2deg) rotateY(180deg);
}

/* ── Faces ── */

.letter-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  padding: 2rem 3rem;
  background-color: #f5f0e8;
  background-image:
    linear-gradient(180deg, rgba(0, 0, 0, 0.02) 0%, transparent 4%),
    linear-gradient(180deg, transparent 96%, rgba(0, 0, 0, 0.03) 100%);

  box-shadow:
    0 1px 2px rgba(0, 0, 0, 0.2),
    0 4px 12px rgba(0, 0, 0, 0.3),
    0 16px 48px rgba(0, 0, 0, 0.45),
    inset 0 0 60px rgba(0, 0, 0, 0.04);

  border-radius: 2px;
  overflow: hidden;

  font-family: 'Caveat', cursive;
  font-size: clamp(1.15rem, 2.5vw, 1.45rem);
  color: #2a2420;
  line-height: 1.85;

  display: flex;
  flex-direction: column;
  justify-content: safe center;
}

/* Paper texture */
.letter-face::before {
  content: '';
  position: absolute;
  inset: 0;
  filter: url(#paper-noise);
  opacity: 0.035;
  pointer-events: none;
  mix-blend-mode: multiply;
}

/* Fold line */
.letter-face::after {
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  top: 48%;
  height: 1px;
  background: linear-gradient(
    90deg,
    transparent 4%,
    rgba(0, 0, 0, 0.05) 15%,
    rgba(0, 0, 0, 0.07) 50%,
    rgba(0, 0, 0, 0.05) 85%,
    transparent 96%
  );
  pointer-events: none;
}

.letter-front {
  z-index: 2;
}

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

/* ── Text lines ── */

.letter-line {
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.6s ease, transform 0.6s ease;
  margin-bottom: 0.15em;
}

.letter-line.revealed {
  opacity: 1;
  transform: translateY(0);
}

.letter-line.signature {
  margin-top: 1.5em;
  font-weight: 700;
  font-size: 1.1em;
}

.letter-line.signature + .letter-line.signature {
  margin-top: 0.2em;
}

/* ── Flip button ── */

.flip-btn {
  background: none;
  border: 1px solid rgba(255, 255, 255, 0.15);
  border-radius: 50%;
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: border-color 0.3s ease, transform 0.3s ease;
  flex-shrink: 0;
}

.flip-btn:hover {
  border-color: rgba(255, 255, 255, 0.4);
}

.flip-btn.flipped {
  transform: rotate(180deg);
}

.flip-arrow {
  width: 20px;
  height: 20px;
  color: rgba(255, 255, 255, 0.4);
  transition: color 0.3s ease;
  transform: rotate(-90deg);
}

.flip-btn:hover .flip-arrow {
  color: rgba(255, 255, 255, 0.7);
}

/* ── Responsive ── */

@media (max-width: 600px) {
  .letter-face {
    padding: 2.5rem 2rem;
  }

  .letter {
    transform: rotate(-0.6deg);
  }

  .letter.flipped {
    transform: rotate(-0.6deg) rotateY(180deg);
  }

  .scene {
    gap: 1.5rem;
  }
}