Hey,
The fixed header cuts off the section headline completely and often parts of the content, especially when a section starts with an image or on lower resolutions, like in this example (there may be worse offenders, I simply quickly grabbed this from the Wikipedia homepage):
{F18650687}
https://de.wikipedia.org/wiki/Blitz?useskin=timeless#Dauer,_Stromst%C3%A4rke_und_Polarit%C3%A4t_von_Blitzen
As a user, I want to see which section I am currently reading after clicking on a section in the table of contents or after clicking on a Wikipedia article link with a section anchor reference in its URL and I want all section text to be fully visible without having to scroll up.
I think there is no super clean solution to this problem, the best way would likely be a JavaScript event handler which overrides the default browser behavior and scrolls the page to the right position with the header offset in mind.