SASS Mixin: tons de cinza para as massas

@mixin grayscale( $toggle: "on", $percentage: 1 ) {
    $svg-type: "matrix";
    $svg-value: "0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0";
    $ie-alpha: alpha(#{"opacity="}round( $percentage * 100 ) );

    @if $percentage != 1 {
        $svg-type: "saturate";
        $svg-value: $percentage;
    }

    @if $toggle == "on" {
        filter: url("data:image/svg+xml;utf8,<svg >); // Firefox 10+, Firefox on Android
        filter: gray $ie-alpha; // IE6-9
        -webkit-filter: grayscale( round( $percentage * 100% ) ); // Chrome 19+, Safari 6+, Safari 6+ iOS
        filter: grayscale( round( $percentage * 100% ) ); // Catch-all
    }

    @if $toggle == "off" {
        @if $svg-type == "saturate" {
            filter: none;
        } @else {
            filter: url("data:image/svg+xml;utf8,<svg >);
        }
        -webkit-filter: grayscale(0%);
        filter: grayscale(0);
    }
}