The Equilateral Triangle of a Perfect Paragraph is a theory developed by Matej Latin in the Better Web Type course about web typography for web designers and web developers. Too many of them still set line-height, font size and line width as independent features when in fact they should all be considered together. The equilateral triangle is a perfect representation of how the three features work in harmony. The theory is explained in details in an article on CSS-Tricks.
This game elaborates on the theory and puts it into practice. Its goal is to teach you about the three features that need to be considered for a perfect paragraph and help you train your eye.