Using the css-injector is fast and easy without knowing each specific directory but if you want compete access is css customization i strongly suggest using the ftp account. Find and edit using the crablabster.php or the netbean.net again it depends in the environment which is comfortable to you.
Best practice go to root dir for complete access and control on your code.
Advantage of css-injector
1.)You can create individual folder in each changes your create in your css.
2.) Save time in editing simple code without going to your ftp account then into your code editor such as netbeam.net