@mixin size($size) {
    @if length($size) == 1 {
        @if $size == auto {
            width: $size;
            height: $size;
        } @else if unitless($size) {
            width: $size + px;
            height: $size + px;
        } @else if not(unitless($size)) {
            width: $size;
            height: $size;
        }
    }

    // Width x Height
    @if length($size) == 2 {
        $width: nth($size, 1);
        $height: nth($size, 2);

        @if $width == auto {
            width: $width;
        } @else if not(unitless($width)) {
            width: $width;
        } @else if unitless($width) {
            width: $width + px;
        }

        @if $height == auto {
            height: $height;
        } @else if not(unitless($height)) {
            height: $height;
        } @else if unitless($height) {
            height: $height + px;
        }
    }
}
