site-header img (img) / "site logo"

I’d like to have the what is called the “site logo” (in “customize/customize/site identity”), appear without space to the top and left of the browser window and without space between the menu bar. I’m implementing this in a child theme and looked at .site header img in style.css. and have a test implementation as follows:

.site-header img
{
margin-left: -20px;
margin-bottom:-25px;
margin-top:-25px;
}
This does not work in all cases; when making the screen smaller space will appear at the top and between the menu bar and img. Please advise. Thanks