Add CSS stylesheets to a module (CKEditor)

There are several ways to do that.

1. Styling a programmatically created block.

1.1 Add a librarie.

 -> Create a file modulename.libraries.yml

-> Add css file, Exemple:

my-block-styling:

  version: 1.x

  css:

    theme:

      css/style.css: {}

1.2 Create CSS file and put it in to the module_folder/css/style.css

1.3 Attach librarie to the block

In your build() methode, add to the output array,

    $output[]['#attached']['library'][] = 'modulename/my-block-styling';

Add / Attaching a library from a Twig template

{{ attach_library('MODULENALE/my-style') }}

To remove a style sheet

stylesheets-remove:

  - '@classy/css/components/tabs.css'

  - core/assets/vendor/normalize-css/normalize.css

Add to a form:

$form['#attached']['library'][] = '<YOUR_THEME_NAME>/<library_name>';

Add CSS Style to CKEditor WYSIWYG

Example:

<?php

use Drupal\editor\Entity\Editor;

/**

 * @param array $css

 * @param Editor $editor

 */

function mymodule_ckeditor_css_alter(array &$css, Editor $editor) {

  $css[] = drupal_get_path('module', 'mymodule') . '/css/ckeditor.css';

}

Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 theme