<center style="margin-top: 200px;">
<p style="font-weight: bold;"><a href="https://google.com/">Link a google, funziona meglio se il link è lungo</a></p>
</center>

a {
    color: blue;
    display: inline-block;
    position: relative;
    text-decoration: none;
    transition: all 0.15s ease 0s;
    text-align: center;
}
a::before {
    background: currentcolor none repeat scroll 0 0;
    content: "";
    height: 2px;
    left: 0;
    position: absolute;
    right: 0;
    top: 100%;
    transform: scaleX(0);
    transition: inherit;
}
a:active::before, a:hover::before {
    transform: scaleX(1);
}