PHP-CSS方法摆脱外部的内部CSS

I want to create a PHP-CSS approach for my web applications. So I don't need to make any external CSS file, nor internal CSS, neither the inline styles. This approach will work as:

... html code ...

<?php
_c( '
header .nav {
  background: yellow;    
}
header .nav a {
  text-decoration: none;
}
');
?>

... more html code and other php-css chunks ...

The function _c() will keep collecting all php-css chunks from entire application on the go, and finally, write all these chunks in a CSS file, compress or minimize and include using <link .. tag at the end.

This way, I won't need to even see the face of .css file. All my php-css chunks will be available on their related pages. So I won't need to keep a bunch of css files open and edit them.

If I use this approach for a huge application, what could be side effects on usability, performance, memory consumption, speed of app etc?