main.js

function openTab(evt, tabName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].className = tabcontent[i].className.replace(" tabcontent-display", "");
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the button that opened the tab
    document.getElementById(tabName).className += " tabcontent-display";
    evt.currentTarget.className += " active";
    evt.currentTarget.parentElement.prepend(evt.currentTarget);
}