Modify the list of CSS files that will be added to a CKEditor instance.
Modules may use this hook to provide their own custom CSS file without providing a CKEditor plugin. This list of CSS files is only used in the iframe versions of CKEditor.
Front-end themes (and base themes) can easily specify CSS files to be used in iframe instances of CKEditor through an entry in their .info file:
ckeditor_stylesheets[] = css / ckeditor - iframe . css;
array &$css: An array of CSS files, passed by reference. This is a flat list of file paths relative to the Drupal root.
$editor: The text editor object as returned by editor_load(), for which these files are being loaded. Based on this information, it is possible to load the corresponding text format object as returned by filter_format_load().
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_ckeditor_css_alter(array &$css, Editor $editor) {
$css[] = drupal_get_path('module', 'mymodule') . '/css/mymodule-ckeditor.css';
}