Provided that all of the ‘buttons’ in your application already use the HTML <button> tag, this is a simple matter to accomplish:
1. Modify your CSS to include the following:
button{background:#eee url(../images/button.png);}
2. Upload the gradient image that you intend to use. (in this example button.png)
3. Done.
For your convenience, the image I use is available here ()
NOTE: MSIE exhibits some poor caching behaviours when background images are used, look for a post on this elsewhere in my blog.