//
  Hides html text and replaces it with an image.
  If you use this on an inline element, you will need to change the display to block or inline-block.
  Also, if the size of the image differs significantly from the font size, you'll need to set the width and/or height.
  @param img
    the relative path from the project image directory to the image.
  @param x
    the x position of the background image.
  @param y
    the y position of the background image.
=replace-text( !img, !x = 50%, !y = 50% )
  :text-indent -9999em
  :overflow    hidden
  :background
    :image= image_url(!img)
    :repeat no-repeat
    :position= !x !y