After spending quite some time on this section without success, but not being able to find any errors, I turned to the forum, only to find some 37 other postings on this same topic. One suggested trying another browser, so I switched from Firefox to IE and had no trouble except that only the header turned red, not the text. However I got the FCC tick and praise for the correct answer and compared it to what I had written on Firefox, which was identical, but no cigar. So without changing anything on the Firefox submission I hit submit again and hey presto this time it signaled success, except that again, only the header was in red not the text, though I believe the whole point of this exercise was to change the text color. So it appears the lesson I have learnt today with this exercise is that even the teachers sometimes get it wrong.
Worryingly, most of the other 37 posts were dated 2016 and this is now 08/2017, but nothing seems to have been fixed. Or have I got this all wrong?