How to create 'box' for post content

Many blog homepages consist of little post excerpts, which then link to the full post on a separate page.
The excerpts generally consist of a headline, a photo and the author and post info.

All that is pretty automatic, but I’ve noticed some bloggers have jazzed it up a bit by containing all this together in a neat little box.

http://www.whereisjenny.com is a prime example. I understand she is a graphic designer so probably has more skills than the average blogger.

However, I was just wondering how this effect is achieved. Is it all down to some CSS skills or is there a plug-in available that can be installed and edited to display post excerpts in this kind of style?