custom-styles-wordpress-editor.php

<?php
//* Add custom styles to the Styles drop down menu in the TinyMCE Editor
//* @link http://anythinggraphic.net/custom-styles-in-wordpress-editor

function themeit_mce_buttons_2( $buttons ) {
	array_unshift( $buttons, 'styleselect' );
	return $buttons;
}
add_filter( 'mce_buttons_2', 'themeit_mce_buttons_2' );
function themeit_tiny_mce_before_init( $settings ) {
	$style_formats = array(
		array( 'title' => 'Orange Bordered Button', 'inline' => 'span', 'classes' => 'orange-bordered-button button' ),
		array( 'title' => 'Slightly Larger Blue Text', 'inline' => 'span', 'classes' => 'color-blue bigger' ),
	);
	$settings['style_formats'] = json_encode( $style_formats );
	return $settings;
}
add_filter( 'tiny_mce_before_init', 'themeit_tiny_mce_before_init' );