<header class="siteHeader">
            <nav>
                <select id="change_font_size">
                    <option value="200">200</option>
                    <option value="225">225</option>
                    <option value="250">250</option>
                    <option value="275">275</option>
                    <option value="300">300</option>
                </select>
                <ul>
                <li><a href="menu.html">MENU</a></li>
                <li><a href="burritos.html">BURRITOS</a></li>
                    <li><a href="index.html"><img class="header-image" src="assets/Headerlogo1.png"></a></li>
                <li><a href="contact.html">CONTACT</a></li>
                <li><a href="about.html">ABOUT</a></li>
                </ul>
            </nav>
        </header>

.siteHeader {
    background-color: #1c1c1b;
    font-family: 'Yanone Kaffeesatz';
    font-size: 250%;
    height: 100px;
    width: 100%;
    border-bottom: solid;
    border-bottom-color: #009641;
    border-bottom-width: 5px;
    position: fixed;
    line-height: 50px;
    z-index: 1000;
    overflow: hidden;
    transition: all 0.8s ease;
}

$("#change_font_size").change(function() {
    var font_size = $(this).val();
    $('.siteHeader > *').css("font-size", font_size + "%");
});