JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap-responsive.css">
<!------------------------------------->
<!-- TWITTER BOOTSTRAP NAVBAR: START -->

<div class="b_navigation navbar">
    <div class="navbar-inner">
        <div class="container">

            <a class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse">
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </a>

            <a class="brand" href="#">Sample</a>

            <div class="nav-collapse">
                <ul class="nav">
                    <li class="active"><a href="#">Dashboard</a></li>
                    <li><a href="#about">Control Panel</a></li>
                    <li class="dropdown" id="nav-dropdown-user">
                        <a class="dropdown-toggle" data-toggle="dropdown" href="#nav-dropdown-user">
                            <i class="icon-user icon-white"></i> <?php echo $username ?>
                            <span class="caret"></span>
                        </a>
                        <ul class="dropdown-menu">
                            <li><a href="#">Profile</a></li>
                            <li class="divider"></li>
                            <li><a href="<?php echo base_url('login/logout') ?>">Sign Out</a></li>
                        </ul>
                    </li>
                </ul>
            </div>
        </div>
    </div>
</div>

<!-- TWITTER BOOTSTRAP NAVBAR: END -->
<!----------------------------------->

<div class="sidebar navbar-height-dependent"></div>
<div class="content navbar-height-dependent"></div>

CSS

@import url('http://twitter.github.com/bootstrap/assets/css/bootstrap.css');
@import url('http://twitter.github.com/bootstrap/assets/css/bootstrap-responsive.css');

.navbar-height-dependent {
    position: absolute;
    top: 40px;
    bottom: 0;
}

.sidebar {
    background: rgba(0,0,0,0.8);
    left: 0;
    right: 80%;
}

.content {
    background: rgba(0,0,0,0.4);
    left: 20%;
    right: 0;
}

JavaScript

$('.navbar').on('show', navbar_height_dependant_toggle)
            .on('hide', navbar_height_dependant_toggle);

function navbar_height_dependant_toggle(e) {
    var height    = e.type == 'show' ? '+=' : '-=';
    var speed    = e.type == 'show' ? 350 : 150;
    height += $(this).find('.nav-collapse').prop('scrollHeight');
    $('.navbar-height-dependent').animate({'top': height}, speed);
}