Maintaining CSS styling after moving div with nested divs from one site to another

[Dulce]

We have two similar-looking sites and would like to copy the content from one site (Site #1) to the other site (Site #2) without breaking the CSS stying for either. Once this is done, Site #1 will be shut down.

To be more specific, the site we are keeping (Site #2) is a WordPress site. We'd like to grab all the inner content from Site #1 and paste it into a WordPress page/post on Site #2, while retaining the formatting for both.

Here are the CSS files for each site:

Site #1 (primary.css and green.css) - We'll be moving everything within the #container div to Site #2.

Site #2 (style.css)

I've combined the CSS files from Site #1 into one CSS file, called it content.css, and uploaded it to WordPress (Site #2). I then created a new template in WordPress that strips out all sidebars in WordPress and includes 1) the header, 2) the call to the new CSS file (content.css), and 3) the footer.

What I'd like to have happen is to be able to copy the container div from the old site (Site #1), copy it to Site #2, and tada, the div and all it's nested divs appear correctly on the new site. However, I need to figure out a way to apply the newly added CSS to only the new content / div.

Any suggestions? I hope that all makes sense.