I am new to CSS and really have little idea how to use it to modify an existing theme. I can easily change colors by replacing the hex’s but beyond that I am lost. I would love to build a theme that utilized outlines (a box) for certain text and understand how to work with margins etc. I do not expect anyone here to tutor me but a link to the basics to fool with would be wonderful. Any help would be doggone nifty! I took a try at css.horse with one of my themes and was lost immediately.
Definitely take a look at some of our Themes that have a border on posts, with margins and everything. Otherwise I find MDN is a great resource for learning about CSS!
Then css.horse is great for trying out what you learn in real-time on your blog – playing with the styles there will immediately show you exactly what they do. If you have any specific questions, please feel free to ask here!