addButton.js

var button = document.createElement('button');
button.id="toogleChatButton";
button.innerHTML="Toogle Chat";
button.addEventListener('click', function() {
    var str = 'only-chat';
    if (document.body.classList.contains(str))
    {
        document.body.classList.remove(str);
    }
    else
    {
        document.body.classList.add(str);
        if (document.getElementsByClassName('bc-chat-messages-container').length != 0)
            document.getElementsByClassName('bc-chat-messages-container')[0].style.top = 0;
    }
});
document.body.appendChild(button);