I had the same problems with the changeover, actually it is quite simple (step by step from my German DW):
When you change a font or a font color this window opens and you can set your options here:
Now you can use/match your new css rule "TextRe20px":
It's seen here:
... and here a little example for you:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>New Color aso</title>
font-family: Verdana, Geneva, sans-serif;
Here is my new text.
short answer, yes you should for a new css-rule, normally.There are some other ways, one of them I'll show you when you want to change an existing rule. Look here:
Clicking ENTER after a semicolon DW opens this menu. Now you are free to choose from, there are plenty of choices, what means you/we have to deal with their different impacts.
Of course you can also open the CSS-style window (translated from German DW: window > CSS-style (Shift + F11).
P.S. (OT)Nice to see German words. Ich würde mich natürlich sehr freuen, wenn ich Dir mit meiner kleinen Erläuterung helfen konnte.