Twenty Ten: Show Background Between Posts?

In Twenty Ten, I want my “custom” body-background image to show between posts, like this:

https://schwarttzy.com/

Schwarttzy accomplished that with the following CSS:

#content {
background:url("images/75.png") repeat scroll 0 0 transparent;
border:3px solid #4A4646;
width:600px;
}

I don’t see a similar bit of CSS in Twenty Ten, but Firebug suggested the possibility of using the .hentry selector:

.hentry {
	background:url("images/blacktrans.png") repeat scroll 0 0 transparent;
}

And here’s how that comes out on my “test” blog:

https://johndimick.com/

But, being a noob, I’m not sure if this is the right thing to do. I have no idea what “hentry” is about (and Google isn’t much help).

Here’s my “real” blog, derived from the Pixel theme, which shows my aim a little better:

https://www.guitarist.com/blog/

I don’t want to take any more chances with my “real” blog — it’s messed it up enough already! — so I’m experimenting with a Twenty Ten child theme on the test blog. If I can get it looking good, I’ll switch my real blog over to the Twenty Ten child.

So am I on the right track using “hentry” for this effect?

Any help will be greatly appreciated!