Additional functions in functions.php of the child theme (instead of  a plugin like TinyMCE Custom Styles): // Prepare tiny_mce for custom styles – Attach callback to ‚tiny_mce_before_init‘ add_filter( ‚tiny_mce_before_init‘, ‚my_custom_styles‘ ); function custom_editor_styles() { add_editor_style(‚editor-styles.css‘); } add_action(‚init‘, ‚custom_editor_styles‘); //add custom styles menu function add_style_select_buttons( $buttons ) { array_unshift( $buttons, ’styleselect‘ ); return $buttons; } //…