Why is my fixed header not working on the Dawn theme 9.0?

[Omar_Issawi]

Hello, I wanted to make my Header Background Transparent Which actually worked well. Now i got the problem that i want to Fix my Header ( so it wont scroll down). I am Using the Dawn Theme 9.0. I have already tried several Online Solutions, which all didnt worked well.

my Website is: www.sonictouch.de

[Omar_Issawi]

No password needed, the website is already online.