@mixin fixed($top: null, $right: null, $bottom: null, $left: null) {
    position: fixed;

    @if ($top != empty) {
        top: $top;
        right: $right;
        bottom: $bottom;
        left: $left;
    }
}

@mixin relative($top: null, $right: null, $bottom: null, $left: null) {
    position: relative;

    @if ($top != empty) {
        top: $top;
        right: $right;
        bottom: $bottom;
        left: $left;
    }
}

@mixin absolute($top: null, $right: null, $bottom: null, $left: null) {
    position: absolute;

    @if ($top != empty) {
        top: $top;
        right: $right;
        bottom: $bottom;
        left: $left;
    }
}