How to make the text-decoration: underline; shorter?

Question

How can I make to make the underline shorter, like in the photo.

And also hot to put a bit of space between the underline and Markets. Here's my code:

#a1:hover {
    color: #55e691;
    text-decoration: underline;
}

Answer 1

#a1 {
    display: inline-block;
    color: rgb(31, 31, 31);
    font-size: 20px;
    font-weight: 700;
    text-decoration: none;
}
#a1,
#a1 div {    
    -webkit-transition: .5s all;
            transition: .5s all;
}
#a1:hover {
    text-decoration: none;
    color: #55e691;
}
#a1:hover div {
    width: 70%;
    height: 3px;
    background-color: #55e691;
    margin: 0 auto;
}

<a id="a1" href="">Markets
    <div></div>
</a>

If you can add som HTML you can enclose a tag in a <div>. There's more than one way

#a1,
.shorter-underline div {
    color: rgb(31, 31, 31);
    text-decoration: none;
}
#a1,
.shorter-underline div {
    -webkit-transition: .5s all;
            transition: .5s all;
}
.shorter-underline {
    display: inline-block;
    font-size: 20px;
    font-weight: 700;
}

#a1:hover {
    text-decoration: none;
    color: #55e691;
}

.shorter-underline:hover div {
    width: 80%;
    height: 3px;
    background-color: #55e691;
    margin: 0 auto;
}

<div class="shorter-underline">
    <a id="a1" href="">Markets</a>
    <div></div>
</div>

Answer 2

a {
  font-weight: 300;
  display: inline-block;
  padding-bottom: 5px;
  position: relative;
  font-weight: bolder;
}
a:hover::after{
  content: "";
  position: absolute;
  width: 50%;
  height: 1px;
  bottom: 0;
  left: 25%;
  border-bottom: 1px solid red;
}

<a>Markets</a>