Customizing the "category" meta on single posts

Hello,

I'm trying to use a customization from another site here that allows to bring the category meta on top of posts and then customize its layout, but this CSS doesn't seem to work the same at this site.

I first use this snippet that bring the category on top and that works fine.

add_filter( 'generate_header_entry_meta_items', function( $items ) {
    if ( is_single() ) {
		$items = array(
			'categories',
			   'date',
			'author',
        );
    } return $items;
} );

But then, those 2 CSS snippets don't work with that site anymore:

/* plain text prefixes for posts meta */
.single .cat-links a:before {
    content: 'Category:';
    margin-right: 0.5ch;
}

.single .cat-links a:after {
    content: ' -';
    margin-right: 0.5ch;
}

I provide both links in information box.

Thanks!