Hi,
You must admit that this is a very general question, so it'll be impossible to give you specific, detailed advice.
"Order process/workflow" - are you referring to the checkout? What exactly do you want to change?
Generally,
this documentation
is already very helpful, particularly the CSS section if it's only about colors and other "look & feel" things.
Anyway, without an exact description of what it's about, what you want to achieve, best documented with screenshots (and/or mock-ups of your goals), and ideally a link to your site, it's impossible to help.