how to make sticky post same width as normal post coraline

Hi,
I need some help to edit the Coraline theme. I’ve used a sticky to keep certain posts at the top of the page but I don’t like the yellow background. I figured out how to edit the CSS to change the background to white so that it fits in with the rest of the page.
But now the post looks a little weird because the text area is much narrower than the normal posts. Is there a simple way to change the width of the sticky posts so that the text is the same width as for the other posts?
The website is nessancleary.co.uk
Thanks for any suggestions,
Nessan