sorry for the confusion 😉
I now removed all my custom css and all other changes which are related to the look of the page.
Now, the main problem is related to the header and the footer of the page.
As you can now see on my homepage, the header has a white background instead of a transparent.
The settings for the footer are the same but the background is transparent.
Even if I change the pattern in “Styling” -> “Header and Footer pattern” nothing happens and the background of both remains the same.
Thanks for your help.