.progress-track {
    position: relative;
    width: 260px;
    height: 6px;
    background: #3a3a3a;
    border-radius: 3px;
    overflow: hidden;
}

.progress-segment {
    position: absolute;
    top: 0;
    width: 30%;                 /* length of the moving segment */
    height: 100%;
    background: #4a90d9;
    border-radius: 3px;
    animation: sweep 3s ease-in-out infinite;
}

@keyframes sweep {
    0%   { left: -30%; }         /* start off-screen left */
    50%  { left: 100%; }         /* fully off-screen right */
    100% { left: -30%; }         /* sweep back left */
}