make the image box across top of Pages fixed

I’ve managed to find the image in the file manager. It’s called nav.jpg. But I can’t figure out how to make it not scale when I adjust the size of the browser window. I know that this is a fancy feature and is part of what makes it responsive, but I just need a static image that doesn’t scale. I’m fine making an image that is super wide and goes all the way across as a browser grows, that’s fine, I just can’t have it distort the image.

Anyone know how to help me please?