Automatically change the colour of slug-related icons?

Hello everyone

I have created an icon for each slug set in the Category menu, and now I have to get WP to automatically change the color of the icons for newly created slugs. As a possible workaround, I created style.php and added the following line to the template PHP file:

<link rel=”stylesheet” type=”text/css” href=”./css/style.php”>

And style.php contains the following:

<? echo “.”.$slug.”{background: #rr0000;}” ?>

Then, when I check the same css in the browser, I see that nothing have been returned for $slug as below:

.{background: #rr0000;}

This is despite the fact that $slug is defined as follows in the template php file:

$categories = get_the_category();
foreach($categories as $category) {
$slug = $category->slug;}

I’m completely stuck as to why $slug cannot call a slug ID. Could someone please help me find what could be used to display slug IDs in css?

Thank you in advance