Steps to reproduce: 1) Open page http://michal.illich.cz/ 2) Change zoom level Results: Central box has still the same size. Note: Font size is changed properly and size of image in bottom right corner is also changed properly, just the central box is not scaled.
See also discussion in bug 407495, it seems related to that.
This is not something we want to fix in general. See the discussion in 407495.