JSFiddle - React, Tailwind, and code Playground

HTML

<ul id="mainNav">
    <li class="navItem">
<a class="navLink" id="activeLink">Link 1</a>

    </li>
    <li class="navItem">
<a class="navLink">Link 2</a>

    </li>
    <li class="navItem">
<a class="navLink">Link 3</a>

    </li>
</ul>

CSS

* {
    font-family: Arial;
    font-size: 14px;
    list-style: none;
    margin: 0;
    padding: 0;
    text-decoration: none;
}

#mainNav {
    background: RGB(200, 230, 240);
    border-bottom: 1px solid RGB(0, 0, 0);
    height: 30px;
    margin: 0 auto;
    position: relative;
    width: 100%;
}
.navItem {
    display: block;
    float: left;
    position: relative;
}
.navItem:last-child .navLink {
    border-right: 1px solid RGB(0, 0, 0);
}
.navLink {
    border-bottom: 1px solid RGB(0, 0, 0);
    border-left: 1px solid RGB(0, 0, 0);
    display: inline-block;
    height: 30px;
    line-height: 30px;
    padding: 0 15px;
    white-space: nowrap;
}
.navItem:hover .navLink {
    background: RGB(120, 200, 250);
    color: RGB(255, 255, 255);
    cursor: pointer;
    font-weight: bold;
}
#activeLink {
    background: RGB(90, 170, 220);
    color: RGB(255, 255, 255);
    font-weight: bold;
}
#activeLink:hover {
    background: RGB(110, 190, 240);
}
.navItem:hover .subNav {
    display: block;
}