That is pure if somone works it out i will be astonished. Ima flag it for any help.
In short, the error is not your code, it's the finickiness of CC. Please reset your zoom in the browser you are using then re-try the lesson submission: Please note the instructions give you how to do this =)
If you're having trouble with font sizes, reset your browser's zoom by pressing Cmd-0 or Ctrl-0.
This is what is causing your error, your zoom must not be right for you to pass the lesson, you can easily re-produce this error if you alter your zoom on that lesson =)
If you continue to receive the error please clear your cache also or try another browser altogether just to make sure, paying careful attention to the zoom still on each try.
It is not, some browsers (chrome and also safari i believe) a have minimum font-size setting, which is set to 12px, do a google search: change minimum font-size chrome (or disable instead of change, if you want to disable minimum font-size all together)