[RESOLVED] css with php

[c_owl]

hi can anyone help me please i need to change the background of my page everyday, but im having a problem with css.
i understand the you cant use php in a ccs style file
i have tryed a couple of ways but getting know were with this.

div#header {
    color: #9C9CFE;
    background: #303030 url(header.jpg) no-repeat;
    height: 180px;
    width: 100%;
} 

i need to change header.jpg ever time, i have tryed

div#header {
    color: #9C9CFE;
    background: #303030 url(<?php  $picheader;?>) no-repeat;
    height: 180px;
    width: 100%;
}

but it will not work.
$picheader will have the background pictures path, this will change ever day..