@mixin media($media, $dir: 'max') {
    @if type-of($media) == number {
        // SCREEN SIZES
        @if $media == null {
            @content;
        }
        @else {
            @media (#{$dir}-width: $media) {
                @content;
            }
        }
    } @else {
        // BROWSERS
        @if $media == 'ie' {
            @media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {
                @content;
            }
        }
        @if $media == 'ff' {
            @-moz-document url-prefix() {
                @content;
            }
        }
    }
}