I'm creating a Twitter Bootstrap main nav and sub nav with a drop down menu on the main nav. The problem is that I can never get the drop down menu to be shown above the sub nav. Here is the HTML:

<div class="mainnav navbar navbar-fixed-top navbar-inverse">
    <div class="navbar-inner">
        <div class="container">
            <ul class="nav">
                <li class="dropdown">
                    <a href="#" class="dropdown-toggle" data-toggle="dropdown">
                        Settings
                    </a>
                    <ul class="dropdown-menu">
                        <li><a>test 1</a></li>
                        <li><a>test 2</a></li>
                    </ul>
                </li>
            </ul>
        </div>
    </div>
</div>

<div class="subnav navbar navbar-fixed-top">
    <div class="navbar-inner">
        <div class="container">
            <ul class="nav">
                <li><a>foo</a></li>
                <li><a>bar</a></li>
            </ul>
        </div>
    </div>
</div>

CSS:

.subnav {
    top: 40px;
}

.mainnav .dropdown-menu {
    // how can I show this menu above the subnav???
}

?