:root {
    --primary: #fff;
    --bg-color: rgb(30, 186, 213);
    --bg-envelope-color: #f5edd1;
    --envelope-tab: #eedaa2;
    --envelope-cover: #edcb90;
    --shadow-color: rgba(0, 0, 0, 0.2);
    --txt-color: #444;
  }
  
  body {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    background: var(--bg-color);
    display: flex;
    align-items: center;
    justify-content: center;
  }
  
  .container {
    height: 100vh;
    display: grid;
    place-items: center;
  }
  
  .container > .envelope-wrapper {
    background: var(--bg-envelope-color);
    box-shadow: 0 0 40px var(--shadow-color);
  }
  
  .envelope-wrapper > .envelope {
    position: relative;
    width: 400px;
    height: 250px;
  }
  
  .envelope-wrapper > .envelope::before {
    content: "";
    position: absolute;
    top: 0;
    z-index: 2;
    border-top: 150px solid var(--envelope-tab);
    border-right: 200px solid transparent;
    border-left: 200px solid transparent;
    transform-origin: top;
    transition: all 0.5s ease-in-out 0.7s;
  }
  
  .envelope-wrapper > .envelope::after {
    content: "";
    position: absolute;
    z-index: 2;
    width: 0px;
    height: 0px;
    border-top: 150px solid transparent;
    border-right: 200px solid var(--envelope-cover);
    border-bottom: 100px solid var(--envelope-cover);
    border-left: 200px solid var(--envelope-cover);
  }
  
  .envelope > .letter {
    position: absolute;
    right: 17.5%;
    bottom: 0;
    width: 60%;
    height: 80%;
    background: var(--primary);
    text-align: center;
    transition: all 1s ease-in-out;
    box-shadow: 0 0 5px var(--shadow-color);
    padding: 20px 10px;
  }
  
  .envelope > .letter > .text {
    font-family: 'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;
    color: var(--txt-color);
    text-align: justify;
    font-size: 7px;
  }
  
  .flap > .envelope:before {
    transform: rotateX(180deg);
    z-index: 0;
  }
  
  .flap > .envelope > .letter {
    bottom: 100px;
    transform: scale(1.5);
    transition-delay: 1s;
  }

  @media (max-width: 768px) {
    .envelope-wrapper {
        width: 100%;
        max-width: 450px;
    }

    .letter {
        width: 80%;
        padding: 15px;
    }

    .text {
        font-size: 12px;
    }

    .envelope::before {
        border-top: 100px solid var(--envelope-tab);
    }

    .envelope::after {
        border-top: 100px solid transparent;
        border-right: 150px solid var(--envelope-cover);
        border-left: 150px solid var(--envelope-cover);
    }
}