Header Distorted

Hell guys,

thats my page:

https://www.babbablog.de

The header picture is totally overstretched now, although I′ve uploaded it as 340 x 113 PNG .

If I read the source code correctly, my understanding is that it is set so that its size is supposed to fit the device. Just open my site on your mobile and you′ll see that everything is working fine. Just the desktop version is a mess.

Can you help?

Thank you so much!