Try hover, active, zoom in, or zoom out in different browsers.
It takes too many codes to make cross-browser shadow and round corner effects. It's just a button but the amount of tags equals to a div module.
The CSS file size is really huge. The effects such as shadow and round corner for Internet Explorer browsers (before version 9) take a lot of codes. Very inefficient.
Internet Explorer browsers don't support some pseudo class well, so we use JavaScript to enhance it.