Adding a border around all posts code

Just to say, I have 2.9.2, but it’s not an option up there.

I’m using the HOPE theme (highly modified) and wanting to differentiate the posts from the background (see http://www.bayton.tk to understand what I mean!)

I have a “header” “wrapper” and “footer” for the post already made up, but I just need to find the code to write and where to put it!

The border needs to wrap around each individual post on the homepage, and the whole post on a post page (both types have the sidebar and are the same width, just different lengths.

The wrapper needs to repeat down, not across.

I very much hope someone can help, I’m losing my marbles on google searches 🙂

Thanks, as per usual in advance for your awesome support
Jason