brgeorgina,
I use developer tools to research and study any area of a web page or site that I’d like to edit or just understand. You select one for your browser and then can see what the css is, and where it is –
(https://developer.chrome.com/devtools)
You can then look it up, learn about how to change it, go from there…
the W3C is a good place to research various syntax (http://www.w3.org/)
For my particular sidebar, the editing would be of course, in the stylesheet, under “class=”sidebar-container”
(I create a child theme for all edits so when updates come out to the theme, they don’t get written over)