pad(y = 100px)
  padding unit(y, 'px')

body
  pad(5px)
  pad()
  pad(10px)
  pad(1)
  pad()

pad-x(n)
  n = unit(n, 'px')
  padding-left n
  padding-right n

pad-y(y)
  padding-top n = unit(y, 'px')
  padding-bottom n

pad(x, y)
  pad-x(x)
  pad-y(y)

form
  pad(5, 10)