Create a PHP/CSS file

//Change to appropriate global variable
<?php global $authority; ?>

<style type="text/css">

//Basic CSS can go in here if need be. 
body.custom-background {
background-color: white !important;
}  

//Example of PHP creating CSS
<?php if($authority['center-logo'] == '1') { echo "#logo img {margin: auto;}"; } ?>

</style>