sticky header

Hi to all Customizr specialists,

I’m trying to get a “true” sticky header without any transition effectts.
Tried numerous CSS-changes in my child theme, but there is still a transition in the header (it shrinks several pixels and sometimes flickers) while scrolling…
n e idea how to solve this issue? – I just want the header to stay the same size on scrolling and no transition at all.

site: http://www.metallico.at

thx, Ben