Cacher is the code snippet organizer for pro developers

/**
 * The lead paragraph text
 *
 * If you choose the 'Lead Paragraph' formatting from the TinyMCE editor a <p>
 * with the class of .lead is applied to it.
 */
.lead {
	font-size: 120%;
}

<?php

/**
 * TinyMCE Formatting
 *
 * Adds a pagraph around selected text with a class of .lead.
 *
 * @param  array $settings Array of TinyMCE settings
 * @return array           Array of TinyMCE settings
 */
function mwtsn_tinymce_formatting( $settings ) {
	$style_formats = array(
		array(
			'title'   => 'Lead Paragraph',
			'block'   => 'p',
			'classes' => 'lead',
			'wrapper' => false,
		),
	);
	$settings['style_formats'] = json_encode( $style_formats );
	return $settings;
}
add_filter( 'tiny_mce_before_init', 'mkdo_tinymce_formatting' );