I think it is the same as my problem.
CSS 7/10 consists of four steps to change "font-size". The first two work fine and you can continue to the third step.
Now, let's get some experience using rem values.
In main.css, for the p selector, add:
Code in main.css:
When you click "run" it changes the font size but does not unlock the "next" button to continue to step 4.
Can you see anything wrong here?