I see a font tag so I assume you tried to change the text font? I can add that into the code and you can just highlight the font and change it to a different one (I put in Verdana), like with the size (I chose 20px). I also see a size font on the "Hello!" so I can add to that, too.
Note that it does matter where you place the tags, you can look at that more carefully in the code.
I didn't change anything- it just comes out like that when I post it.