Em is a scalable unit, 1 em is equal to the current font size of the current element, parent elements can effect em values
Percent is a scalable unit similar to Em, the only difference is the Em units scale faster when Text-Size stuff
Point is a physical unit length (1/72 of an inch)
Pixel is a unit of length in screen pixels
Rem is similar to the Em, it is a scalable unit. 1 rem is equal to the font size of the root element
Enum representing the different font size units https://developer.mozilla.org/en-US/docs/Web/CSS/font-size