Here is a good tutorial by Silver Thistle on how to upload a header image: Customizing BookLikes Tutorial - Part 2 - Back to basics. Adding a new header
And here's the code I used to make mine the width of the page:
The yellow part used to say: repeat-x;
So, you could search for that in the HTML.
I wrote in: no-repeat; width; 100%; background-size; 100%;
I don't know if this is the right way to do it. I just typed a bunch of different things until something worked. This looks like it's working but...
If there is something wrong with this code or there is a better way to do this would some nice programmer please tell me?