* {
    box-sizing: border-box;
  }

  body > ul {
    position: absolute;
    top: 50%;
    width: 800px;
    height: 200px; 
    left: 50%;
    margin-left: -400px;
    margin-top: -130px;
  }
 
  ul > li {
    width: 25%;
    list-style-type: none;
    position: absolute;
    top: 0;
    padding: 20px;
    height: 200px; 
    opacity: 0;
    padding-top: 40px;
    text-align: center;
    transition: 1s opacity; 
  }

  .active {
    opacity: 1;
  }