The button to open the side menu disappears, why?

Question

Bootstrap

I am using Jasny Bootstrap. You need to make a side menu that opens on the click of a button.
Here is the menu code:

<header>
    <nav id="myNavmenu" class="navmenu navmenu-inverse navmenu-fixed-left offcanvas" role="navigation">
        <a class="navmenu-brand" href="index.html">Football Clubs</a>
        <ul class="nav navmenu-nav">
            <li class="active"><a href="index.html">Home</a></li>
            <li><a href="about.html">About</a></li>
            <form class="navbar-form navbar-right">
                <div class="form-group has-feedback" id="loginDiv">
                    <input type="text" class="form-control" placeholder="LOGIN" name="login">
                    <span id="loginSpan" class="glyphicon form-control-feedback"></span>
                </div>
                <div class="form-group has-feedback" id="passwordDiv">
                    <input type="password" class="form-control" placeholder="PASSWORD" name="password">
                    <span id="passwordSpan" class="glyphicon form-control-feedback"></span>
                </div>
                <button type="button" class="btn btn-success" onclick="loginForm(this.form)">ENTER</button>
            </form>
        </ul>
    </nav>
    <div class="navbar navbar-inverse navbar-static-top">
        <button type="button" class="navbar-toggle" data-toggle="offcanvas" data-target="#myNavmenu" data-canvas="main">
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
        </button>
    </div>
</header>

The problem is that the button to open the menu only appears when the window is sized for smartphones.
How to fix it?
ps tried to implement an example: www.jasny.net/bootstrap/examples/navmenu-push