Space between header en browser

Can you post a link to the site in question?

sorry, forgot!

https://www.eenwebsitevanbas.nl/

Do you mean the space between the navigation menu and the blue bar beneath it?

the space between the top of the browser and my name

If you want the name flush against the top of the viewport you could add:
margin-top: -5px; to #site-title

but is it not possible without a minus margin?

Another possibility is to set the line-height on #site-title
line-height: 2em;

ah k! works, thanks!!

No problem at all, glad I could help.