What: Building text sizes on a fixed ratio (e.g. 1.25) instead of arbitrary sizes.
Why: A single ratio makes hierarchy feel harmonious and intentional, not random.
How: Start from the body size (16) and multiply up by the ratio for headings (20, 25, 31…).
Common mistake: Picking sizes that 'look good' with no relationship, so they clash.
Exercise: Redesign a page with three sizes built on one ratio and compare it to the original.