I had used something similar for a background of an image, but now for the buttons on my site it is not working anymore.
nav#menu li:hover {
display: inline-block;
transition-duration:0.3s;
**-webkit-transition-duration: 0.3s;**
**-moz-transition-duration: 0.3s;**
**-ms-transition-duration: 0.3s;**
**-o-transition-duration: 0.3s;**
background-color: #6A6A6A;
padding: 10px;
margin: 2px;
(excerpts in bold serve for compatibility with older versions of browsers)