Nice idea. I like it.
Some general feedback:
Too much clicking.
Intrusive ‘success’ popup/overlay becomes jarring after a few times.
The step by step structure of the exercises feels a bit dated. I wonder how this would look like as a one-page game where you progress down the page fluidly (ideally by never leaving the input field), rather than having to click through a series of standalone exercises.
Maybe guiding the user through using all of these features in markdown from an empty document would be better than these focused exercises. Just an idea.