disclaimer: i’m not css/html expert.
I believe that browsers render web pages in x,y co-ordinates (width, height) however they also keep the z-index. The z-index is somewhat controlled by css code. The performance of the page rendering is also controlled by how deep the content is i.e. depth of the displayable html element. Performance degrades as we move the elements deep inside the container elements. e.g.
I tried to play with the browser (‘Firefox’) tool and found very interesting web page architectures (because they look like amazing colorful physical designs) of google and HN home pages.
feel free to explore the gallery below: