It’s perfectly normal to define two or three parameters, what happens then depends on number of parameters you give.
With 2 parameters, first one is responsible for vertical values (top, bottom) and second parameter is horizontal (left, right).
With 3 it gets a bit more tricky. But basically, first parameter is then top, second param is responsible for both horizontal values (left, right) and last one is bottom.
Also I would like to add, since we’re discussing units here, that you can mix units freely, e.g.
padding: 10px 20% 5em 0;