Toggling a panel and the clicker text
Please check out this updated jsFiddle: https://jsfiddle.net/b4mp044z/5/

I've changed your JS code into :

$(document).ready(function () {    
    $("#panelSub").hide();

    $("#toggleSubjects").click(function () {
        $("#panelSub").slideToggle("slow");                
        $(this).find('i').toggleClass('fa-arrow-circle-down fa-arrow-circle-up')
    });
    return false;
});


and updated your HTML and CSS to hold all your structure and content. It's a good practice to keep things separated (HTML, CSS and JS)