<div class="navbar">
        <h3>OmniFoods</h3>
        <a href="#home">Home</a>
        <a href="#about">About</a>
        <a href="#contact">Contact</a>
</div>

.navbar {
    height: 50px;
    width: 100%;
    font-family: Arial;
    position: fixed;
    background: transparent;
    color: #fff;
    top: 0;
    left: 0;
}

.navbar h3 {
    float: left;
    margin-left: 30px;
    margin-top: 20px;
}

.navbar a {
    float: right;
    padding: 18px;
    margin-right: 30px;
    text-decoration: none;
    color: #333;
}

window.onscroll = function() {
    var navbar = document.getElementsByClassName('navbar')[0];

    if(window.pageYOffset > 100) {
        navbar.style.background = "#fff";
    }
    else {
        navbar.style.background = "transparent";
    }
}