Different font sizes can be in a golden ratio. Let’s say the body-font size on your website is 16px. The header-font size could be a golden-ratio multiple of your body size — that is, it could be 16 φ = 16 x 1.618 = 25.88 or roughly 26px. 

Some also use the golden ratio to determine the line height needed for a particular font size to be in a golden ratio. (The line height is the font height plus the white space between lines of text — it basically governs how tightly arranged the lines of text are in a paragraph.) For example, if you had a font size of 16px for your body copy, the line height could be 16 φ = 16 x 1.618 = 25.88 or, again, roughly 26px.