Since `input` elements don't support `:before` and `:after`, we have to rely on using multiple backgrounds. IE8 doesn't support this. IE9 does, but doesn't support gradients (without filter).

So we would have to use a combination of `filter:` and `background-image`, but this usually either breaks IE8, or IE9, or both.

Since an icon is more important than a gradient, I removed the filter and use only the icon. IE8 has the nasty habit of trying to load multiple background-images (even though it doesn't support it) when filters are defined, so we have to define an extra rule for IE8 in tweaks.css that "resets" the background.

I'll update it if I find a better solution.