$(document).ready(function() {
$(".expandable-content").on('click', function(){
    $(this).children(".internal-content").slideToggle();
});


$(".menu-button").on('click', function(){
    var position = $(".blue-box").css("left");
    if( position == "0px") {
        $(".blue-box").velocity({left: "250px"}, 500);
        $('.side-nav-link').finish();
        $('.side-nav-link').velocity('transition.slideUpIn', { stagger: 50 });
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        $('.side-nav-link').finish();
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});

<div class="blue-box">
        <h1>Julian Ptak</h1>
        <h2>Kempis Coder. Simplicity. Purity.</h2>
        <div class="menu-button"><img class="button-icon" src="img/menu-icon.png"><p class="button-text">Menu</p></div>
    </div>

    <div class="red-box">
        <ul class="side-nav">
            <li class="side-nav-link"><a href="">Home</a></li>
            <li class="side-nav-link"><a href="">Work</a></li>
            <li class="side-nav-link"><a href="">Hobbies</a></li>
            <li class="side-nav-link"><a href="">Writings</a></li>
            <li class="side-nav-link"><a href="">Code</a></li>
            <li class="side-nav-link"><a href="">Contact</a></li>
        </ul>
    </div>