Underline active navbar links in bootstrap 4

Question

I'm upgrading a website from bootstrap 3 to 4 (beta). The css I used to underline active navbar links is no longer working. Instead of underlining the item, it underlines the full width of the page. How can I underline active nav items in bootstrap 4?

Bootstrap 3 css

.navbar-default .navbar-nav > .active:after {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    content: " ";
    border-bottom: 5px solid #5BC0EB;
}

Attempted Bootstrap 4 css

.navbar-light .navbar-nav .active::after {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    content: " ";
    border-bottom: 5px solid #5BC0EB;
}

HTML

<nav class="navbar fixed-top navbar-light bg-light navbar-expand-md">
    <div class="container">
        <a class="navbar-brand" href="#">My Website</a>

        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse"
            aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
        </button>

        <div class="collapse navbar-collapse justify-content-end" id="main-nav-collapse">
            <ul class="navbar-nav">
                <li class="nav-item active"><a class="nav-link" href="#about">About</a></li>
                <li class="nav-item"><a class="nav-link" href="#classes">Classes</a></li>
                <li class="nav-item"><a class="nav-link" href="#gallery">Gallery</a></li>
                <li class="nav-item"><a class="nav-link" href="#events">Events</a></li>
                <li class="nav-item"><a class="nav-link" href="#contact">Contact</a></li>
                <li class="nav-item"><a class="nav-link" href="#offers">Offers</a></li>
            </ul>
        </div>
    </div>
</nav>

Answer 1

This happened because of your positioning.

Try to set relative position to your li and set after to a tag inside li which will be absolute positioned like below

.navbar-nav > li {
  float: left;
  position: relative;
}
.navbar-light .navbar-nav .active a::after {
  border-bottom: 5px solid #5bc0eb;
  bottom: -10px;
  content: " ";
  left: 0;
  position: absolute;
  right: 0;
}

Hope it helps.