I found an easier fix.
I simply used a text widget.
Then I looked for the code for an image source. I think I found it on the W3 site.
Then I copied that code into the text box.
Then I went to the image, clicked on it, and copied the file URL.
And then it was a case of a little experimentation with putting the URL into the source code.
So now it works.
No widget and no CSS.