A good way of "learning" is to do this:
Create a new folder inside your css_styles folder which holds the folders:
classic
default
dark
web wiz
So create a new folder and name it whatever, example in this case -
officeorange

Then COPY and paste the two files from your default folder called default_style and printer_style and pop them into your new folder called officeorange so you now have this:

The next step then takes time. Open up your copied default_style file in your new officeorange folder (DO NOT RENAME IT) using
Araneae which is FREE and does a good enough job. Don't try editing the file using web creation software as it tends to muck up the coding

And you will see how the coding appears. The steps to changing the colours, fonts, etc take time as you work you way through it, but it is great to create new skins. As you change hex codes you should upload the new file and "test" what has changed. That way you can break it down step by step
Alternatively send me some cash

and I'll take up some of my time sorting it

(just kidding)
You can
view more examples here