Q:

Can I use file_get_contents to load css? 

Instead of this: 
<head>
    <link rel="stylesheet" type="text/css" href="css_file.css" />
</head>

I want to do this:
<head>
    <style><?php file_get_contents("css_file.css");?></style>
</head>

For some reason though, the text shows up in the doc but the style is not applied.  This is a two part question:

Why is this not working? 
Is this a bad idea to do this? 

A:

This does what you'd like todo, output will be your css file, use something like preg_replace if you need to have more readable content, you might want to add new lines for example, before and after { }, I tested both without preg_replace and the examples are working well with a simple css file, I did not test it with complex css files but it should work as well, I kindly ask to try it with your css files.  I hope it will help you into the right direction...
<? php
$css_File = file_get_contents("css_file.css"); // Can use single quot as well...
echo '<style type="text/css">' .  $css_File . ' </style>'; // All php echo example
? >

OR much better example, I think this could be what you want:
<? php $css_File = file_get_contents('http://www.example.com/css_file.css'); ? >
<style type="text/css"><?php echo $css_File; ? ></style><!--// your request example //-->

A:

This question was posted when I was a beginning developer.  I didn't know about Sass and other easier and better ways to achieve variables in CSS.  I also didn't know about browser caching. 
Jeremy Karlsson answered the question in a comment.  file_get_contents requires echo.