fix menue while scrolling

For the named Website we would like to ask, if its possible to have the menue field where the Logo and the upper menue appears stay fixed or sticky on the screen and moves while scolling down the page?
Is there any css code or some thing to make the menue filed sticky? I′ve tried some plugins but they wont work with this theme.

Thanks for your help!

The page I need help with: [log in to see the link]