How to make active link underlined (CSS)?

Solution for How to make active link underlined (CSS)?
is Given Below:

I wanted to make a nice underlined menu on website and I found code like below.
It’s cool animated but can anyone tell me how to make active link underlined to make visitors sure on which page they are?

    list-style: none;
}
li {
    display: inline-block;
    padding: 20px 0 20px;
    vertical-align: middle;
}
a:hover, a:focus, a:active {
    color: #999;
    text-decoration: none;
}
a {
    font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;
    text-decoration: none;
    transition: color 0.1s, background-color 0.1s;
}
a {
    position: relative;
    display: block;
    padding: 16px 0;
    margin: 0 12px;
    letter-spacing: 1px;
    font-size: 12px;
    line-height: 16px;
    font-weight: 900;
    text-transform: uppercase;
    transition: color 0.1s,background-color 0.1s,padding 0.2s ease-in;
    color: #000;
}
a::before {
    content: '';
    display: block;
    position: absolute;
    bottom: 3px;
    left: 0;
    height: 3px;
    width: 100%;
    background-color: #000;
    transform-origin: right top;
    transform: scale(0, 1);
    transition: color 0.1s,transform 0.2s ease-out;
}
a:active::before {
    background-color: #000;
}
a:hover::before, a:focus::before {
    transform-origin: left top;
    transform: scale(1, 1);
}``` 

Add a class called “active” to your active a element like so:

<li class="active"><a href="index.html">Text</a></li>

Then add this to your CSS:

a.active{
text-decoration: underline;
}

a.active:hover, a.active:focus, a.active:active{
text-decoration: underline;
}

I would not do what any other answer says.
(First of all, I’m not a novice WordPress user, but I have experience in CSS)
If you want something along the lines of this:
Preview

Then, a span <span></span> with nothing in it should do. Then in CSS change the peramiters all you like!

   display:block;
   width:100% /*or whatever width you want the effect of <hr>*/
   border-top: 1px solid #ccc'