// Add custom CTA styles to TinyMCE editor
if ( ! function_exists('tdav_css') ) {
	function tdav_css($wp) {
		$wp .= ',' . get_bloginfo('stylesheet_directory') . '/css/tinymce.css';
		return $wp;
	}
}
add_filter( 'mce_css', 'tdav_css' );

http://wordpress.org/support/topic/how-do-i-add-custom-stylesheets-to-tinymce

A little function to add custom styles to the tinymce editor in wordpress.

Add custom styles to visual editor Wordpress

wordpress

PHP