Custom CSS file generation in WordPress

custom-file.php

<?php

// OUTPUT CUSTOM CSS FILE
function stag_link_custom_styles(){
  $output = '';
  if(apply_filters('stag_custom_styles', $output)){
    $perma_structure = get_option('permalink_structure');
    $url = home_url(). '/stag-custom-styles.css?'.time();
    if(!$perma_structure) $url = home_url(). '?page_id=stag-custom-styles.css';
    echo '<link rel="stylesheet" href="'.$url.'" type="text/css" media="screen" />';
  }
}
add_action('wp_head', 'stag_link_custom_styles', 15);

// CREATE CUSTOM CSS FILE
function stag_create_custom_styles(){
  $perma_structure = get_option('permalink_structure');
  $show_css = false;

  if($perma_structure){
    if(!isset($_SERVER['REQUEST_URI'])){
      $_SERVER['REQUEST_URI'] = substr($_SERVER['PHP_SELF'], 1);
      if(isset($_SERVER['QUERY_STRING'])){$_SERVER['REQUEST_URI'].='?'.$_SERVER['QUERY_STRING'];}
    }
    $url = (isset($GLOBALS['HTTP_SERVER_VARS']['REQUEST_URI'])) ? $GLOBALS['HTTP_SERVER_VARS']['REQUEST_URI'] : $_SERVER['REQUEST_URI'];
    if(preg_replace('/\\?.*/', '', basename($url)) == 'stag-custom-styles.css') $show_css = true;
  }else{
    if(isset($_GET['page_id']) && $_GET['page_id'] == 'stag-custom-styles.css' ) $show_css =  true;
  }
  if($show_css){
    $output = '';
    header('Content-Type: text/css');
    echo apply_filters('stag_custom_styles', $output);
    exit;
  }
}
add_action('init', 'stag_create_custom_styles');

?>