JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="nav">
    <li><a href="index.php">home</a></li>
    <li><a href="custHelp.php">who we are</a>
    <ul>
        <li id="changeBG1"><a href="about.php">about</a></li>
        <li id="changeBG2"><a href="help.php">team</a></li>
    </ul>
</li>

CSS

a:link {
    background-color: blue;
}

.active{
    background-color: red;
}

JavaScript

var url = window.location.href;
url = url.substr(url.lastIndexOf("/") + 1);

// For this example only
url = "about.php";
////////////////////////

$("#nav a[href$='" + url + "']").addClass("active");