tinymce-docs/_includes/configuration/body_class.md

body_class

Use the body_class option to add a class to the body of each editor instance. This class can be used to override the styles added by the content_css option. The body_class will be removed if the editor is removed and will not be included in any content retrieved from the editor.

Type: String

Example: Using body_class

This will add the same class to all editors that gets created by the init call.

tinymce.init({
  selector: 'textarea',  // change this value according to your HTML
  body_class: 'my_class'
});

This will set specific classes on the bodies of specific editors.

tinymce.init({
  selector: 'textarea',  // change this value according to your HTML
  body_class: 'elm1=my_class, elm2=my_class'
});