honestly, "your headers font size should be 16px instead of 16px"
have you tried a so-called Refresh of your Browser
under certain circumstances you can shoot your Browser in an
Therefor it is of an advantage to know that you have 2 reset facilities:
One is the use of the F5-key which does a refresh Browser
Two, select© your code
Then use the Reset Code button of the course-window,
then paste your code back in.
Always refresh the browser after making corrections:
CTRL f5 ( if on Windows or Linux)
CMD r ( if on a MAC).
Please don't use language like that in the title of your post, thanks.