@mixin screen($sWidth) {
    @if $sWidth == big {
        @media (max-width: 1000px) { @content; }
    }
    @else if $sWidth == middle {
        @media (max-width: 800px) { @content; }
    }
    @else if $sWidth == small {
        @media (max-width: 500px)  { @content; }
    }
}