a{
  text-decoration: none;
}
a{
 position: relative;
  display: inline-block;
  transition: .3s;
}

a::after {
  position: absolute;
  bottom: 0;
  left: 50%;
  content: '';
  width: 0;
  height: 2px;
  background-color: #fd7e00;
  transition: .3s;
  transform: translateX(-50%);
}

a:hover::after{
  width: 100%;
}