how to put php code in css code example

Example 1: css php

<?php
  header('Content-type: text/css');
  /*
    Hier werden Variablen und ggf.
    Algorithmen festgelegt.
  */
?>

body {
  background-color: #ffffff;
  color: #000000;
}

Example 2: adding css to php file

echo "<link rel='stylesheet' type='text/css' href='CSS/main.css'>";