Embed page not referencing CSS

Hi, I’m trying to set up a WP site to run alongside our church’s main site so auxiliary groups can have direct access to posting news and things without mucking up our main site.

On our main site, we have a sidebar with three different elements, each listed as separate html documents (though I believe they’re parsed as PHP – here’s where I’m getting in over my head) that are referenced throughout the site. I want to include these elements on the WP site’s sidebar – so far, I’ve simply embedded the html document’s URL in an iframe with the Text widget. Good news – the text shows up; bad news – it’s not referencing the proper CSS for the div. See the WP site here.

I copied the relevant CSS code from our main site and pasted in the WP theme’s main CSS document (there are three total CSS files that I can see – rtl, style, & editor-style) – no success there. If you could point me in the right direction, I would appreciate it greatly – thanks!