h2 {
    font-size: 2em;
    position: relative;
    padding: 0 5px;
    align-self: center;
}
h2:before, h2:after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    bottom: 0;
    background: black;
    transition: .3s ease-out;
}
h2:before {
    left: 150%;
}
h2:after {
    right: 150%;
}
h2.expand:before, h2.expand:after {
    width: 150%;
}