media_in_mixin_in_mixin.scss

@mixin getMediaDimensions() {
    @content;
}

@mixin getDimensions() {
    @include getMediaDimensions() {
        @media (min-width: 768px) {
            body {
                height: 50px;
                @content;
            }
        }
    }
}

@include getDimensions() {
    width: 50px;
}