German translation tweaks

[incompl]

• use "ß" where appropriate, as in "große" (not "grosse")
• Beware the Deppenleerzeichen: e.g. "CSS-Grundlagen" needs a hyphen. I'd suggest the same for words like "Box-Model", unless you keep the english term, but then I'd spell it all lowercase: "box model"
• Always have a space after comma, period etc.