style.css

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #ff9a9e, #fad0c4);
  font-family: 'Arial', sans-serif;
  overflow: hidden;
}

.container {
  perspective: 1000px;
}

.envelope {
  position: relative;
  width: 300px;
  height: 200px;
  cursor: pointer;
  transform-style: preserve-3d;
  transition: transform 0.5s ease-in-out;
}

.flap {
  position: absolute;
  width: 0;
  height: 0;
  border-left: 150px solid transparent;
  border-right: 150px solid transparent;
  border-bottom: 100px solid #ff6f61;
  transform-origin: top;
  transition: transform 0.5s ease-in-out;
}

.body {
  position: absolute;
  bottom: 0;
  width: 300px;
  height: 100px;
  background: #ff6f61;
}

.message {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  color: #fff;
  opacity: 0;
  transition: opacity 0.5s ease-in-out;
}

.message h1 {
  font-size: 24px;
  margin-bottom: 10px;
}

.message p {
  font-size: 18px;
}

.envelope.open .flap {
  transform: rotateX(180deg);
}

.envelope.open .message {
  opacity: 1;
}

/* Background Animation */
@keyframes moveBackground {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}

body {
  background: linear-gradient(-45deg, #ff9a9e, #fad0c4, #fbc2eb, #a6c1ee);
  background-size: 400% 400%;
  animation: moveBackground 10s ease infinite;
}