Changing One Box On Website Skeleton

Hello, I have a pricing plan that was included with the skeleton I downloaded. I want to change ONE of the boxes to a certain color so that the plan box is ORANGE instead of GREEN. Look at picture for reference.

Where would I dig into in order to make this change? Thx. Screen Shot 2017-03-10 at 2

That's going to require some CSS to override the current color styling. Usually this is done by putting more specific CSS in a custom.css file. There is some general information on this in the docs

How do I add a new css class to the box?

Thx.

if you want to add another css class you would just need to edit the relevant twig file in the theme's templates/ folder. The best way to find which one, is to use a good editor (ST3, Atom, VisualStudio Code, etc) and search for something, that should uncover the file you are looking for.