CSS was redone a bit to use grids, which are better for this use case and scale better on mobile devices.
There's also flexbox code for browsers that don't support grids.
There's also fallback, legacy flexbox code for even older browsers; this was tested on RetroZilla, which is based on Firefox 2.0. Most browsers (NetSurf has been tested and fails) made in the past 15 years should now be able to correctly view the site.