[rimantas]

  Q: What methods do you know to realize columns?
  A: cleardiv
  clearfix (better one)

WTF? I'd expect floats, faux columns, display: table-* , *-column-count being the answer but get some cleardiv/clearfix instead. I never liked those, especially cleardiv. Often you can do simply reusing next element (#footer {clear:both}), but sometimes that's not enough, alas.

In my opinion any competent frontend developer should know these, not enough for the hero. On the other hand, to be able to interview hero you should be at least on that level yourself, which is not the case there, imho.