body {
    margin: 0;
    overflow: hidden;
    background: black;
    color: lime;
}

canvas {
    display: block;
}

.font {
    font-family: 'Courier New', Courier, monospace;
    text-align: center;
}

.btn-index{
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
  
  a{
    display: block;
    width: 200px;
    height: 40px;
    line-height: 40px;
    font-size: 18px;
    font-family: 'Courier New', Courier, monospace;
    text-decoration: none;
    color: #0F0;
    border: 2px solid #0F0;
    letter-spacing: 4px;
    text-align: center;
    position: relative;
    transition: all .35s;
  }
  
  a span{
    position: relative;
    z-index: 2;
  }
  
  a:after{
    position: absolute;
    content: "";
    top: 0;
    left: 0;
    width: 0;
    height: 100%;
    background: #0F0;
    transition: all .35s;
  }
  
  a:hover{
    color: #000000;
  }
  
  a:hover:after{
    width: 100%;
  }

  p {
    font-size: 20px;
  }