Add CSS to the WP Theme Customizer toolbar

Hello I have added a <div> as an option to the WP Theme Customizer toolbar, I intend this to show different CSS background options using the css background-image: -webkit-gradient rendering however I have found no way to add the CSS, the add_action( 'wp_head') does not seem to allow update to the toolbar.

The code below works and ads a <div> to the background color tab but this is as far as I have got.

Please help.

function mytheme_customize_register( $wp_customize ) {
	class Example_Customize_Textarea_Control extends WP_Customize_Control {
		public $type = 'textarea';

		public function render_content() {
			?>
				<div id="css1">xx</div>

			<?php
		}
	}

	$wp_customize->add_setting( 'textarea' );

	$wp_customize->add_control(
		new Example_Customize_Textarea_Control(
			$wp_customize,
			'textarea',
			array(
				'label' => 'Textarea',
				'section' => 'colors',
				'settings' => 'textarea'
			)
		)
	)
}