This is basic info and a mini-lesson on the Elements tab of Chrome Dev Tools. Check out more in-depth documentation here: developers.google.com/web/tools/iterate/inspect-styles/basics
We will be using the webpage mckellen.com/ per suggestion of Free Code Camp user kmiasko.
If you right click and select 'Inspect element', you can have access to the elements tab. You can change text, background color, text color, and any other CSS or HTML you'd like!
These changes don't set up automatically, so don't use this as an IDE or a place to create or edit anything you want to save. You can set up something called 'persistent authoring' to save.
Cascade, inherit, and other CSS rules still apply, so keep that in mind as you play around. Additionally, overridden styles will be shown as having a strike through them.
Padding, border, and margins are easily inspected and edited using the colorful box on the right or bottom side.
Please check out the Chrome Dev Tools documentation at http://developers.google.com/web/tools/chrome-devtools/