Webleb - HTML UI Elements -

@property --flap-rotation {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}

@property --progress {
  syntax: "<percentage>";
  inherits: false;
  initial-value: 20%;
}

@property --text {
  syntax: "<number>";
  inherits: false;
  initial-value: 0.0;
}

* {
  box-sizing: border-box;
}

body {
  height: 1000vh;
}
.text-to-show {
  animation: reveal-text ease both;
  animation-timeline: scroll();
  animation-range: 80%;
  opacity: var(--text);
}
.envelope {
  container: envelope / inline-size;
  perspective: 1000px;
}

.flap {
  clip-path: polygon(100% 0%, 0 0%, 50% 100%);
	width: 100cqw;
	height: 30cqw;
  transform-style: preserve-3d;
  rotate: x var(--flap-rotation);
  transform-origin: 50% 0;
  animation: animate-flap ease both;
  animation-timeline: scroll();
  animation-range: 0 60%;
  z-index: 4;
  position: relative;
}

.face {
  clip-path: polygon(50% 35%, 100% 0, 100% 100%, 0 100%, 0 0);
}

.heart {
  --c: red;
  position: absolute;
  width: 50cqw;
  left: 50%;
  top: 0;
  transform: translateY(var(--progress));
  animation: show-heart ease both;
  animation-timeline: scroll();
  animation-range: 60%;
  margin-left: -25cqw;
  aspect-ratio: 1/1;
      z-index: 3;
  background:

radial-gradient(at 70% 31%,var(--c) 29%,#0000 30%),
   radial-gradient(at 30% 31%,var(--c) 29%,#0000 30%),
   conic-gradient(from -45deg at 50% 84%,var(--c) 90deg,#0000 0) 
    bottom/100% 50% no-repeat;
}

@keyframes animate-flap {
  from {
    --flap-rotation: 0deg;
  }
  99% {
    z-index: 4
  }
  100% {
    --flap-rotation: 180deg;
    z-index: 1;
  }
}

@keyframes show-heart {
  from {
    --progress: 20%;
  }
  to {
    --progress: -90%;
  }
}

@keyframes reveal-text {
  from {
    --text: 0.0;
  }
  
  to {
    --text: 1.0;
  }
}

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