I know you can add a value with css with [ ] bit. But can I overwrite one? In which case I would need the ability to use !important. And I need to give it a background image.

Google custom search is using the "Search" value in my input. In their demo though they use a search icon instead. I wish to use this icon instead. My attempt looks like this...

input.gsc-search-button[value=""] {
background:url(http://www.google.com/uds/css/v2/search_box_icon.png)
}