wp_get_custom_css() WordPress Function

function wp_get_custom_css( $stylesheet = '' ) {
	$css = '';

	if ( empty( $stylesheet ) ) {
		$stylesheet = get_stylesheet();
	}

	$post = wp_get_custom_css_post( $stylesheet );
	if ( $post ) {
		$css = $post->post_content;
	}

	/**
	 * Filters the custom CSS output into the head element.
	 *
	 * @since 4.7.0
	 *
	 * @param string $css        CSS pulled in from the Custom CSS post type.
	 * @param string $stylesheet The theme stylesheet name.
	 */
	$css = apply_filters( 'wp_get_custom_css', $css, $stylesheet );

	return $css;
}