$background-image-fade-in-time: $default-animation-basic !default;

@keyframes fade-in {
    0%   { opacity: 1; }
    100% { opacity: 0; }
}

.u-background-image-fade-in--loaded {
    position: relative;
    &:after {
        content: '';
        @include fill-parent();
        opacity: 0;
        background-color: inherit;
        animation: fade-in $background-image-fade-in-time;
    }
}