How do I add a picture to the top bar?

When loading my blog, https://www.kgeiger.net
you will see the URL kgeiger.net load in the top bar. Instead of having the Url that links to the main page of my blog, I want to have an image displayed.

I went into wp-layout.css and changed the header to

#header {
background: transparent;
background-image: url (https://www.kgeiger.net/images/kgeiger_large.jpg);

And that did nothing.

And I attempted to mess with the index.php but yah I do not know what I am doing apparently. Can anyone give me a quick summary of what I need to do.
Thanks