Why is there still a margin/padding at the top when printing?

[pstein]

Lets talk on the following (simplified) example webpage:

https://blogs.systweak.com/uninstall-unwanted-programs-on-windows-10/

I did now the following:

- I opened Firefox--WebDeveloper

- I deleted the element <header class="site-header">....    </header> in WebDeveloper

- I changed in WebDeveloper all the values for CSS key ".article-shadow" and attributes margin-top, padding and border-radius to 0

As you can see from the following snapshot the headline "Easy Tricks to uninstall Unwanted...." appears in browser window directly below the top border.

http://easycaptures.com/8003064666

Now when I print this page into a pdf then an unexpected big, big gap between top border and headline is inserted.

Why?

Does it come from @media print section?

Which CSS value is responsible (otherwise)?

How can I get rid of the gap in pdf printout

Peter