I want to have a very simple navigation menu. It has to be clickable. So when using this code
Your code is a rather odd mix of plain JS and jQuery. I'd suggest using one or the other. Here's a simple version of your code using jQuery:
$(function() {
$('#navBtn').click(function() {
$('#navContent').toggle();
});
});
#navContainer {
position: relative;
display: inline-block;
}
#navContent button {
display: block;
}