I do it this way:
The html:
The xCss.php:
// place here your vars
$fntBtn = 'bold 14px Arial'
$colBorder = '#556677' ;
$colBG0 = '#ffffdffffd' ;
$colBG1 = '#44ffffdd' ;
$colBtn = '#aaffffdd' ;
// here goes your css after the php-close tag:
?>
button { border: solid 1px = $colBorder; ?>; border-radius:4px; font: = $fntBtn; ?>; background-color:= $colBtn; ?>; }