:root {
  --bg-top: #11162a;
  --bg-bottom: #090b15;
  --kuromi-purple: #7f5dff;
  --melody-pink: #ff6fb3;
  --glow: rgba(255, 255, 255, 0.9);
  --t-flap: 700ms;
  --t-rise: 820ms;
  --t-rise-delay: 280ms;
  --ease-flap: cubic-bezier(0.2, 0, 0.2, 1);
  --ease-rise: cubic-bezier(0.24, 0.84, 0.3, 1);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "VT323", monospace;
  display: grid;
  place-items: center;
  background:
    radial-gradient(circle at 10% 15%, rgba(127, 93, 255, 0.25) 0%, transparent 32%),
    radial-gradient(circle at 90% 10%, rgba(255, 111, 179, 0.22) 0%, transparent 32%),
    linear-gradient(170deg, var(--bg-top), var(--bg-bottom));
  overflow: hidden;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image:
    radial-gradient(circle, rgba(255, 111, 179, 0.18) 2px, transparent 2px),
    radial-gradient(circle, rgba(127, 93, 255, 0.16) 2px, transparent 2px);
  background-size: 75px 75px, 115px 115px;
  background-position: 0 0, 30px 35px;
  opacity: 0.5;
  transition: opacity 500ms ease, filter 500ms ease;
}

.focus-overlay {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 1;
  backdrop-filter: blur(0px);
  background: radial-gradient(circle at 50% 52%, rgba(255, 255, 255, 0) 0%, rgba(127, 93, 255, 0.14) 72%);
  opacity: 0;
  transition: opacity 550ms ease, backdrop-filter 550ms ease;
}

.hearts-layer {
  position: fixed;
  inset: 0;
  pointer-events: none;
  overflow: hidden;
  z-index: 4;
}

.pixel-heart {
  position: absolute;
  bottom: -24px;
  left: 0;
  font-family: "Press Start 2P", monospace;
  font-size: var(--size, 12px);
  line-height: 1;
  color: var(--color, #ff9bd3);
  text-shadow:
    0 0 7px rgba(255, 255, 255, 0.85),
    0 0 14px rgba(255, 111, 179, 0.68);
  opacity: 0;
  will-change: transform, opacity;
  transform: translate3d(0, 0, 0) scale(1);
  animation: heartRise var(--duration, 2100ms) linear forwards;
}

.landing {
  width: min(580px, 92vw);
  text-align: center;
  position: relative;
  z-index: 2;
  transition: filter 450ms ease;
}

.intro {
  margin: 0 0 24px;
  font-family: "Press Start 2P", monospace;
  font-size: clamp(0.62rem, 1.6vw, 0.78rem);
  color: #fff;
  text-shadow: 0 0 8px var(--glow), 0 0 16px rgba(127, 93, 255, 0.72);
  transition: opacity 420ms ease, filter 420ms ease;
}

.envelope-wrap {
  position: relative;
  width: min(460px, 90vw);
  margin: 0 auto;
  perspective: 1200px;
  transform-origin: center bottom;
  animation: envelopeIdle 2.5s ease-in-out infinite;
  transition: transform 520ms ease, filter 520ms ease;
}

.envelope {
  position: relative;
  width: 100%;
  height: 290px;
  border-radius: 14px;
  overflow: hidden;
  filter: drop-shadow(0 20px 32px rgba(8, 10, 20, 0.66));
  isolation: isolate;
  transition: filter 500ms ease;
}

.envelope-back {
  position: absolute;
  inset: 0;
  border-radius: 14px;
  background: linear-gradient(165deg, rgba(15, 20, 39, 0.96), rgba(8, 11, 24, 0.98));
  border: 2px solid rgba(255, 111, 179, 0.26);
  z-index: 0;
}

.letter-panel {
  position: absolute;
  left: 50%;
  bottom: 12px;
  width: 82%;
  height: 88%;
  transform: translateX(-50%) translateY(100%);
  border-radius: 12px;
  background: linear-gradient(180deg, #141a2f, #0f1325);
  border: 2px solid rgba(127, 93, 255, 0.26);
  box-shadow: 0 10px 18px rgba(8, 10, 20, 0.46);
  opacity: 0;
  z-index: 5;
  transition:
    transform var(--t-rise) var(--ease-rise),
    opacity 200ms ease;
}

.letter-panel::before {
  content: "";
  position: absolute;
  inset: 18px 20px;
  background-image: repeating-linear-gradient(
    180deg,
    transparent,
    transparent 22px,
    rgba(255, 255, 255, 0.08) 22px,
    rgba(255, 255, 255, 0.08) 24px
  );
  border-radius: 4px;
}

.letter-panel::after {
  content: "♥";
  position: absolute;
  top: 14px;
  left: 50%;
  transform: translateX(-50%);
  font-family: "Press Start 2P", monospace;
  font-size: 0.7rem;
  color: var(--melody-pink);
  text-shadow: 0 0 8px rgba(255, 111, 179, 0.6);
}

.flap {
  position: absolute;
}

.flap-top {
  top: 0;
  left: 0;
  width: 100%;
  height: 58%;
  background: linear-gradient(155deg, #232a48, #171d34);
  clip-path: polygon(0 0, 100% 0, 50% 100%);
  transform-origin: 50% 0%;
  transform: rotateX(0deg);
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  transition: transform var(--t-flap) var(--ease-flap);
  z-index: 7;
}

.flap-left {
  left: 0;
  bottom: 0;
  width: 50%;
  height: 100%;
  background: linear-gradient(170deg, #1a223f, #12192f);
  clip-path: polygon(0 100%, 100% 100%, 100% 0);
  z-index: 3;
}

.flap-right {
  right: 0;
  bottom: 0;
  width: 50%;
  height: 100%;
  background: linear-gradient(210deg, #1d2544, #131b32);
  clip-path: polygon(0 0, 0 100%, 100% 100%);
  z-index: 3;
}

.flap-bottom {
  left: 0;
  right: 0;
  bottom: 0;
  height: 57%;
  background: linear-gradient(180deg, #1f2748, #141c36);
  clip-path: polygon(0 100%, 50% 0, 100% 100%);
  z-index: 4;
}

.letter-heart {
  position: absolute;
  left: 50%;
  top: 53%;
  transform: translate(-50%, -50%);
  font-family: "Press Start 2P", monospace;
  font-size: 0.92rem;
  color: #fff;
  text-shadow:
    0 0 8px rgba(255, 255, 255, 0.9),
    0 0 14px rgba(255, 111, 179, 0.7);
  z-index: 6;
  transition: opacity 200ms ease;
}

.open-btn {
  position: absolute;
  left: 50%;
  top: 62%;
  transform: translate(-50%, -50%);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  border-radius: 999px;
  padding: 12px 18px;
  min-width: 200px;
  font-family: "Press Start 2P", monospace;
  font-size: 0.56rem;
  color: #fff;
  background: linear-gradient(125deg, var(--kuromi-purple), var(--melody-pink));
  border: 2px solid rgba(255, 255, 255, 0.25);
  box-shadow: 0 12px 24px rgba(127, 93, 255, 0.34);
  text-shadow:
    0 0 7px rgba(255, 255, 255, 0.88),
    0 0 14px rgba(255, 111, 179, 0.6);
  transition:
    transform 0.2s ease,
    filter 0.2s ease,
    box-shadow 0.2s ease,
    opacity 200ms ease;
  z-index: 8;
}

.open-btn:hover {
  transform: translate(-50%, -50%) translateY(-2px) scale(1.02);
  filter: saturate(1.08);
  box-shadow: 0 16px 28px rgba(127, 93, 255, 0.46);
}

.envelope-wrap.opening .open-btn {
  opacity: 0;
  pointer-events: none;
}

.envelope-wrap.opening .letter-heart {
  opacity: 0;
}

.envelope-wrap.opening .flap-top {
  transform: rotateX(-178deg);
}

.envelope-wrap.opening .letter-panel {
  opacity: 1;
  transform: translateX(-50%) translateY(-18%);
  transition:
    transform var(--t-rise) var(--ease-rise) var(--t-rise-delay),
    opacity 180ms ease var(--t-rise-delay);
}

.envelope-wrap.opening .envelope {
  transform: translateY(0) scaleX(1) scaleY(1);
}

.envelope-wrap.opening {
  animation: none;
  transform: translateY(0) scaleX(1) scaleY(1);
}

body.romantic-active::before {
  opacity: 0.24;
  filter: blur(3px);
}

body.romantic-active .focus-overlay {
  opacity: 1;
  backdrop-filter: blur(8px);
}

body.romantic-active .intro {
  opacity: 0.42;
  filter: blur(1.5px);
}

body.romantic-active .envelope-wrap {
  transform: translateY(-8px) scale(1.055);
  filter: saturate(1.08);
}

body.romantic-active .envelope {
  filter: drop-shadow(0 22px 34px rgba(127, 93, 255, 0.42));
}

@keyframes envelopeIdle {
  0%,
  100% {
    transform: translateY(0) scaleX(1) scaleY(1);
  }
  18% {
    transform: translateY(0) scaleX(1.015) scaleY(0.985);
  }
  34% {
    transform: translateY(-8px) scaleX(0.985) scaleY(1.025);
  }
  52% {
    transform: translateY(0) scaleX(1.02) scaleY(0.98);
  }
  68% {
    transform: translateY(-3px) scaleX(0.992) scaleY(1.01);
  }
  84% {
    transform: translateY(0) scaleX(1.008) scaleY(0.992);
  }
}

@keyframes heartRise {
  0% {
    opacity: 0;
    transform: translate3d(0, 0, 0) scale(0.7);
  }
  12% {
    opacity: 0.96;
  }
  100% {
    opacity: 0;
    transform: translate3d(var(--drift, 0px), -115vh, 0) scale(var(--scale-end, 1.12));
  }
}

@media (prefers-reduced-motion: reduce) {
  .envelope-wrap {
    animation: none;
    transform: translateY(0) scaleX(1) scaleY(1);
  }

  .flap-top {
    transition: opacity var(--t-flap) ease !important;
  }

  .envelope-wrap.opening .flap-top {
    transform: rotateX(0deg) !important;
    opacity: 0;
  }

  .pixel-heart {
    animation: none;
    opacity: 0;
  }
}

@media (max-width: 520px) {
  .envelope {
    height: 250px;
  }

  .open-btn {
    min-width: 178px;
    font-size: 0.52rem;
  }

  .envelope-wrap.opening .letter-panel {
    transform: translateX(-50%) translateY(-14%);
  }
}