Why not store padding as :root variables?

In the 3rd course in the HTML/Series, Mosh starts to use variables in the :root {} for colors, border-radius , and other reused values. He does not store paddings and margins, which are reused more than anything. How come this is?

Hi jcm10,
Since padding and margin, cannot be the same for all elements. Imagine building a house with the exact same size materials.