html, body{
    margin: 0;
    padding: 0;
    height: 100%;
    overflow: hidden;
    font-family: sans-serif;
    background: #e0e0e0;
    position: relative;
  }

  #game{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 0;
    background-color:green;
    overflow:hidden;
    cursor:crosshair;
  }