mytheme_custom_fonts

/**
 * Add Flower font to the theme options font list.
 * 
 * @param array $custom_fonts Current custom fonts.
 * @return string[string][string] The Web fonts section.
 */
function mytheme_redux_custom_fonts( $custom_fonts ) {
	return array(
		'Web Fonts' => array(
			‘flower' => 'flower'
		)
	);
}
add_filter( 'redux/option_name/field/typography/custom_fonts', 'mytheme_redux_custom_fonts' );

mytheme_enqueue_scripts

/**
 * Add Flower font stylesheet.
 */
function mytheme_enqueue_scripts() {
	wp_enqueue_style(
		'flower-font',
		get_stylesheet_directory_uri() . ‘/assets/fonts/flower/stylesheet.css'
	);
}
add_action( 'wp_enqueue_scripts', 'mytheme_enqueue_scripts' );