Cross-browser alpha transparent background CSS (rgba) Stylus mixin

transparency.styl

// background transparency
background-transparency(color, alpha = 1)
  ms-color = argb(color, alpha)
  background rgb(color)
  background rgba(color, alpha)
  .lt-ie8 &
    zoom 1
  .lt-ie9 &
    background transparent
    filter s('progid:DXImageTransform.Microsoft.gradient(startColorstr=%s,endColorstr=%s)', ms-color, ms-color)
    &:nth-child(n)
      filter none

hex(decimal)
   hex-value = ('0') ('1') ('2') ('3') ('4') ('5') ('6') ('7') ('8') ('9') ('A') ('B') ('C') ('D') ('E') ('F')
   unquote(hex-value[floor(decimal / 16)] + hex-value[floor(decimal % 16)])

argb(color, alpha = 1)
  unquote('#') + hex(alpha * 255) + hex(red(color)) + hex(green(color)) + hex(blue(color))

Added improvements from https://gist.github.com/adunkman/2580972