@mixin alphaImg($backgroundHeight) {
    $position: calc($backgroundHeight / 2);
    background-size: $backgroundHeight $backgroundHeight;
    background-image: linear-gradient(45deg, #ccc 25%, transparent 25%), linear-gradient(135deg, #ccc 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #ccc 75%), linear-gradient(135deg, transparent 75%, #ccc 75%);
    background-position: 0 0, $position 0, $position (
        -$position),
        0 $position;
}