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$font-size: em($base-font-size, $em-base-grid); // Initial font-size based on browser setting, which is $em-base-grid (default browser 16)
$line-height: em($base-line-height, $base-font-size); // Initial line-height is based on initial font-size

//-------------------
//--- FUNCTIONS -----
//-------------------

@function rhythm($lines:1, $from-size: $base-font-size) {
  @return 1em * ($lines * $line-height) / em($from-size, $base-font-size);
}

@mixin font($to-size, $lines: $to-size/$base-font-size, $from-size: $base-font-size) {
  font-size: em($to-size, $from-size);
  line-height: 1em * ($lines * $line-height) / em($to-size, $base-font-size);
}

//-------------------------------------------------------------------------------
//--- OPACITY IN IE8 CAN BE ACHIEVED USING THE PROPRIATARY FILTER PROPERTY ------
//-------------------------------------------------------------------------------
// @todo check for using opacity for IE5-7 instead of filter
@mixin opacity($opacity) {
  /* IE 8 */
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=#{round($opacity * 100)})";

  /* IE 5-7 */
  filter: unquote("progid:DXImageTransform.Microsoft.Alpha(Opacity=#{round($opacity * 100)})");

  /* Netscape */
  -moz-opacity: $opacity;

  /* Safari 1.x */
  -khtml-opacity: $opacity;

  /* Good browsers */
  opacity: $opacity;
}