Centre Featured Image

Hi! I would like to centre my featured image on my new blog. I’m not knowledgeable with code, but have Googled endlessly and there are tons of code out there for this problem that seem to work for everyone else, however none of them work on my site.

I’m not sure if this makes a difference or not, but at one point the code I tried completely deleted my post. I hope this did not mess things up. I’m waiting until I figure this out to re-post anything, that’s why there is no text on my blog.

Thank you for any help! Also – the theme I am using is X Blog Lite.

The page I need help with: [log in to see the link]