design tweaks in twentytwelve

Looking for some advice. Wondering if anyone has any suggestions on how I can tweak the css in twentytwelve to match the decorative accents I use around the box on the rest of the site (created with illustrator and dreamweaver). Maybe impossible?

The wordpress page is here:
<https://www.victoriapatterson.com/news&gt;

Basically trying to get the little triangle box things around the top and bottom corners of the white box like I do on this page:
<https://www.victoriapatterson.com/index1.html&gt;

I use tables and images to do it on the other pages. It’s a bit of a hack job. Any help or suggestions are greatly appreciated. I’m a total novice.