.clock span {
    font-size: 32px;
    position: relative;
    display: inline-block;
    text-align: center;
}

.clock span::after {
    font-size: 11px;
    position: absolute;
    bottom: -18px;
    left: 50%;
    transform: translateX(-50%);
}

#hrs::after {
    content: 'HOURS';
}

#mins::after {
    content: 'MINS';
}

#secs::after {
    content: 'SECS';
}