.slide-progress-indeterminate {
    background-image: linear-gradient(
        90deg,
        rgba(255, 255, 255, 0) 0%,
        rgba(255, 255, 255, 0.45) 50%,
        rgba(255, 255, 255, 0) 100%
    );
    background-size: 200% 100%;
    animation: slide-progress-shimmer 1.4s linear infinite;
}

@keyframes slide-progress-shimmer {
    from { background-position: 200% 0; }
    to   { background-position: -200% 0; }
}