.pace {
    width: 100%;
    height: 6px;
    background: #2696D3;
    background: linear-gradient(to right, #2696D3 50%, #fff 50%);
    background-size: 200% 100%;
    background-position: right bottom;
    transition: all 2s ease
}

.pace.active {
    background-position:left bottom;
}