phpBB Forum controls float into the next line below the top menu

When viewing the ReactOS Forum as a logged in user on small resolutions, the phpBB controls of the top menu float into the next line.
It would be better if they could occupy two lines of the top menu in this case.

I have no idea how to implement that with pure CSS, so that the current menu look is kept for high resolutions and two lines are occupied as soon as the browser window gets too small.

Attached is a screenshot from forum user dsp8195 that illustrates the problem.