In Drupal 8, how can you have CKEditor load additional stylesheets when using a configured filter format? In Drupal 7, you could give the WYSIWYG module paths to CSS sheets to load, which made the editor text reflect the theme as much as possible. I am not seeing this option.


Here is one way to do it... not sure if there are others (admin based):

 * Implements hook_ckeditor_css_alter().
 * Injects our CSS sheets anytime CKEditor has loaded.
 * @param array $css
 * @param Drupal\editor\Entity\Editor $editor
function mymodule_ckeditor_css_alter(array &$css, Editor $editor) {
  if (!$editor->hasAssociatedFilterFormat()) {

  $known_formats = [

  if (in_array($editor->getFilterFormat()->id(), $known_formats)) {
    $css[] = drupal_get_path('theme', 'mytheme') . '/build/css/style.css';
| improve this answer | |
  • 4
    before function, use Drupal\editor\Entity\Editor; is needed. – user780 Nov 3 '18 at 19:51

Unless you want to load styles for specific formats, you can easily add CSS within your MODULE.info.yml file, like so:

  - css/application.css
  - css/ckeditor.css

Use @import statements inside one of the stylesheets to pull in external stylesheets not in your theme:

/* in css/ckeditor.css */
@import url('//mycdn.com/myfonts.css');
@import url('/path/to/drupal/module/styles.css');
| improve this answer | |
  • 2
    I discovered a workaround to include external stylesheets using an @import statement. – JamesWilson Mar 22 '18 at 17:18
  • 1
    Yes, you can use standard CSS import @import url("http://example.com/file.css"); – Steven Sep 18 '18 at 22:33

Here is a simple solution for this in Drupal 8, when you are using a custom theme or custom admin theme.

  1. Open your custom theme info file *.info.yml and add the line above libraries or below base_theme.

      - css/ckeditor.css
  2. Create a file ckeditor.css in the css/ directory.

  3. Write your CSS in that file and the styles will be applied to CKEditor.
| improve this answer | |

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