Stylesheet not linking

get_template_directory_uri() just returns the directory of the current theme, not the link to the actual stylesheet.

In functions.php try:

function register_directories_style() {
    wp_register_style('style', get_template_directory_uri().'/style.css', [], 1);
    wp_enqueue_style('style');
}
add_action( 'wp_enqueue_scripts', 'register_directories_style');

if you wanted to select a different stylesheet, you just updated the $src arguement. e.g.

function register_directories_style() {
    wp_register_style('directory_style', get_template_directory_uri().'/css/directories.css', [], 1);
    wp_enqueue_style('directory_style');
}
add_action( 'wp_enqueue_scripts', 'register_directories_style');