CSS Alter for Zero Theme

zero_css_alter.php

<?php
/**
 * Implements hook_css_alter().
 */
function zero_css_alter(&$css) {
  $exclude = array(
    'modules/system/system.base.css' => FALSE,
    'modules/system/system.messages.css' => FALSE,
    'modules/system/system.theme.css' => FALSE,
    'modules/system/system.menus.css' => FALSE,
    'modules/comment/comment.css' => FALSE,
    'modules/field/theme/field.css' => FALSE,
    'modules/node/node.css' => FALSE,
    'modules/search/search.css' => FALSE,
    'modules/user/user.css' => FALSE,
  );
  $css = array_diff_key($css, $exclude);
}