Well, partially. It successfully inserts class ‘full-width-post’ into first three posts, but for some reason, it only shows full width posts only under <1000px display. Over 1000px, it shows first post full and rest as masonry.
But the main problem is, that when you click ‘More posts’ aka page 2, it displays another these 3 posts full-width again. And I don’t want it to.