Keeping style for post

https://reviews.sekhu.net/category/film/page/2/

If you go to the above link you’ll note that there is a particulat theme/style used for that page. Click on the post, however reverts to the main page (home) and uses its stylesheet to create the style for the post.

What I want to do is use the same style for film to work for the film related posts, and music realted posts would use the music style sheet etc. What do I need to change, and where do I change, to have posts for a particular category to keep the category style for their posts without going to the main page, and without losing the style I’ve set for that category?

Thanks in advance