Gap between the menu bar and the edge of the screen

Hi Viewing on the PC. When I'm on the main page (at the top) the menu list is at the bottom. There is now a gap between the menu bar and the edge of the screen. I thought this was from my CSS at first and removed it, but the problem persists. How do I get rid of this gap? https://schneegetraenke.ch/ Many thanks for the help regards Heinz