CSS Guidelines, first draft

Hello frontend,

I'm pull requesting this **very first** version of a CSS/SCSS Coding Guideline too start the discussion. Feel free to discuss, change and update the file. In the end, we should merge the result and use the Styleguide from this very moment on.

Requests of further change after this point, should be placed as pull request again and discussed that way. In this repository please use all tools github gives us, like the issue management, gists and so on.

Thx for the attention so far…
Das ist hart :smiley: Bin ich nicht gewohnt.
Ich mag es auf jeden Fall gerne, wenn Eigenschaften inhaltlich gruppiert sind, also z.b. immer `width` und `height` beieinander stehen, oder auch `margin`, `padding`, `border` oder `font-size` und `line-height` etc.