body {
    margin:0;
    background-color:#191919;
    min-height:100vh;
    display:flex;
    align-items:center;
    justify-content:center;
    font-family:Helvetica,Sans-serif;
  }
  a {
    text-decoration:none;
    color:#FFF;
  }
  .rainbow-button {
    width:calc(20vw + 6px);
    height:calc(8vw + 6px);
    background-image: linear-gradient(90deg, #00C0FF 0%, #FFCF00 49%, #FC4F4F 80%, #00C0FF 100%);
    border-radius:5px;
    display:flex;
    align-items:center;
    justify-content:center;
    text-transform:uppercase;
    font-size:3vw;
    font-weight:bold;
  }
  .rainbow-button:after {
    content:attr(alt);
    width:20vw;
    height:8vw;
    background-color:#191919;
    display:flex;
    align-items:center;
    justify-content:center;
  }
  .rainbow-button:hover {
    animation:slidebg 2s linear infinite;
  }
  
  @keyframes slidebg {
    to {
      background-position:20vw;
    }
  }