PHP in CSS file

[eluser]Kemik[/eluser]
Hey all,

This is a bit of a noob question but if I put php in a css file and load the css file as normal will the php run?

Code:

#middle_banner{
width:651px;
height:165px;
margin:auto;
padding:20px 0 0 0;
background:url(images/middle_banner_2.jpg) no-repeat center;
}

PHP's rand() function would be great to select a random middle_banner. I was going to do
middle_banner_<?php rand(2, 6) ?>.jpg

Thanks.