inside the opening "font" tag just put "size=+1" or "size=N" where "N" is in the range 1 (smallest) to 7 (largest). When the browser reaches the closing "font" tag it will revert the the previous size, colour etc. Remember that all HTML tags use American spelling otherwise they don't work.
I have no idea how I did that as I had a comment in red first (Which read - If you think Dawn was a pain just wait till you see me practising this!) and then the second question in large font. The first dispppeared and I got the large red font! So, not as clever as I thought I was!