Just a tip, since you have experience with HTML/CSS. You can clone the client area templates (/app/views/clients/bootstrap/) and name it something else. Then, select the theme under Settings > Company > Look and Feel > Template. This will allow you to modify a clone of the client templates. You'll be able to change it back if you want, and upgrading wont overwrite the new theme. (Though you should run a diff and merge changes)