custom properties with Stylus

fix-to.styl

fix-to(pos...)
  position fixed
  if length(pos) == 2
    {pos[0]} 0
    {pos[1]} 0
  else if length(pos) == 4
    a = pos[0..1]
    b = pos[2..3]
    {a[0]} a[1]
    {b[0]} b[1]
  else
    error('invalid arguments. fix-to: <pos> [n] <pos> [n];')

a#login
  fix-to bottom right

a#login
  fix-to top 5px left 5px

out.css

a#login {
  position: fixed;
  bottom: 0;
  right: 0;
}
a#login {
  position: fixed;
  top: 5px;
  left: 5px;
}