Thanx to all of you – your contributions made my day.
Important: using emdizzle’s recipe has created two bugs:
a) The file name in step 2 is missing an “s”. It should be “new-um-styles.css” as it is used in step 4
b) Copying the text from the browser might bring you to wrong characters being pasted in your editor. Make sure, the text in your editor of choice is really using the string escape character for php (“‘”). At best, use a php code aware editor and check that the text between the “‘” is a string.
With this modifications it runs like a charm. I’ve done this with little experience in CSS. Thanx again!