JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-1.12.1.min.js"></script>
<div class="nav-icon2"></div>

CSS

.nav-icon2 {height: 50px; width: 50px; background-color: #456789; }

JavaScript

var color = '';
var x = $(".nav-icon2").css('backgroundColor');
hexc(x);
alert(color);

function hexc(colorval) {
    var parts = colorval.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
    delete(parts[0]);
    for (var i = 1; i <= 3; ++i) {
        parts[i] = parseInt(parts[i]).toString(16);
        if (parts[i].length == 1) parts[i] = '0' + parts[i];
    }
    color = '#' + parts.join('');
}