.mm-spn span:not(:last-child):after {
    content: '';
    display: block;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    border-right: 1px solid;
    opacity: .15;
} 
.mm-spn span:not(:last-child) {
    width: calc(100% - var(--mm-spn-item-height));
}