If you are refering to your main navigation:
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link meal" href="../Pages/home.html">HOME<span class="sr-only"></span></a></li>
<li class="nav-item "> <a class="nav-link meal" href="../Pages/starters.html">STARTER</a></li>
<li class="nav-item "> <a class="nav-link meal" href="../Pages/mains.html">MAIN</a></li>
<li class="nav-item "> <a class="nav-link meal" href="../Pages/Dessert.html">DESSERT</a></li>
<li class="nav-item "> <a class="nav-link meal" href="../Pages/Events.html">EVENTS</a></li>
</ul>
Then you need to use some javascript to 'mark' the naviagtion link as you go from page to page:
Include the below at the bottom of ALL your pages, just before the closing </body> tag.
<script>
var url = document.URL
var url = url.substr(url.lastIndexOf('/') + 1);
var links = document.querySelectorAll('.navbar-nav li a');
for (var i = 0; i < document.links.length; i++) {
var link = document.links[i].href;
var link = link.substr(link.lastIndexOf('/') + 1);
if (url === link) {
document.links[i].className = 'active';
}
}
</script>
You can also do this using css.