example.css

.box {
  -moz-box-shadow: 5px 9px 5px 5px rgba(0, 0, 0, 0.75);
  -webkit-box-shadow: 5px 9px 5px 5px rgba(0, 0, 0, 0.75);
  -o-box-shadow: 5px 9px 5px 5px rgba(0, 0, 0, 0.75);
  box-shadow: 5px 9px 5px 5px rgba(0, 0, 0, 0.75);
}

example.scss

.box {
  @include photoshop-drop-shadow(120, 10px, 50, 10px, rgba(0, 0, 0, 0.75));
}

photoshop-drop-shadow.scss

@import "compass/css3/box-shadow";
@import "compass/css3/text-shadow";

//--------------------------------
// Photoshop Drop Shadow
//--------------------------------
@mixin photoshop-drop-shadow ($angle: 0, $distance: 0, $spread: 0, $size: 0, $color: #000, $inner: false) {
  $angle: (180 - $angle) * pi() / 180; // convert to radians
  $h-shadow: round(cos($angle) * $distance);
  $v-shadow: round(sin($angle) * $distance);
  $css-spread: $size * $spread/100;
  $blur: ($size - $css-spread);
  $inset: if($inner != false, 'inset', '');
  
  @include box-shadow($h-shadow $v-shadow $blur $css-spread $color unquote($inset));
}


//--------------------------------
// Photoshop Inner Shadow
//--------------------------------
@mixin photoshop-inner-shadow ($angle: 0, $distance: 0, $spread: 0, $size: 0, $color: #000) {
  @include photoshop-drop-shadow ($angle, $distance, $spread, $size, $color, true);
}

//--------------------------------
// Photoshop Text Shadow
//--------------------------------
@mixin photoshop-text-shadow ($angle: 0, $distance: 0, $spread: 0, $size: 0, $color: #000) {
  // NOTE: $spread has no effect for text shadows
  $angle: (180 - $angle) * pi() / 180;
  $h-shadow: round(cos($angle) * $distance);
  $v-shadow: round(sin($angle) * $distance);
  $css-spread: $size * $spread/100;
  $blur: ($size - $css-spread);
  
  @include text-shadow($h-shadow $v-shadow $blur $color);
}