jslirola If you are talking about the grey background, if you don't like that you can add this CSS to your custom CSS in your admin appearance settings. But, if you're talking about the fact that the button does not change color after clicking it, then yes, I can't get that to work.
And, even if this is not what you want I will leave this here for anyone who wants the preview icon to be the icon only.
.item-preview button, item-preview button:hover, item-preview button:active {
background: transparent;
box-shadow: none;
}