generate the middle clamp value by setting min / max screen size

[Ricozor]

Well done, it’s a very nice tool! But I think it might be better if the user only entered the min/max font-size and min/max screen sizes and then the tool returned the clamp();

My first impression was that I would be able to move the handles and lines in the graph and that all the fields would automatically update.

If I have time I will try to make a fork.