Quick enqueue reference

<?php
function skyler_enqueue_styles() {
	wp_enqueue_style(
		'skyler-css',
		get_stylesheet_directory_uri() . '/skyler-style.css',
		array(),
		filemtime(trailingslashit(__DIR__) . 'skyler-style.css'),
		false
	);
}
add_action( 'wp_enqueue_scripts', 'skyler_enqueue_styles' );