Feature request: Define CSS variables

Hi Danny,

Would you consider outputing the font family names as CSS variables? Something like the following:

function test_inline_styles() {

	$body_font    = ogf_build_font_stack( get_theme_mod( 'ogf_body_font' ) );
	$heading_font = ogf_build_font_stack( get_theme_mod( 'ogf_heading_font' ) );

	$css =
	'
	:root {
		--font-body: ' . esc_attr( $body_font ) . ';
		--font-heading: ' . esc_attr( $heading_font ) . ';
	}
	';

	wp_add_inline_style( 'child-style', wp_strip_all_tags( $css ) );
}
add_action( 'wp_enqueue_scripts', 'test_inline_styles' );

This way the theme can use these variables in custom places.

Thanks!

-Kathy