In case this can help anyone, here's simple CSS as a jumping off point. Turns it into a basic rounded square big enough for thumbs with a toggled background color.
input[type='checkbox'] {_x000D_
-webkit-appearance:none;_x000D_
width:30px;_x000D_
height:30px;_x000D_
background:white;_x000D_
border-radius:5px;_x000D_
border:2px solid #555;_x000D_
}_x000D_
input[type='checkbox']:checked {_x000D_
background: #abd;_x000D_
}
_x000D_
<input type="checkbox" />
_x000D_