Hey Mike,
Ths for reply. I do it like you say, but still is the same.
Maybe I did not explain it clearly to you.
I first made a widget named “header”, in which I add image. After that, I add some css code found here in one post:
#header .widget {
left: 50%;
padding-top: 0;
position: absolute;
top: 0;
transform: translate(-50%);
z-index: 999;
}

inserting your code into the function.php nothing happens, everything is the same.
I’m using child theme and I put code into function.php of child theme.