Main sidebar

<div style="padding: 10px; height: 400px; border: 1px solid black">
    <nav class="sidebar">
        <ul id="level-1" class="sidebar-group-primary">
            <li class="card">
                <a href="#first-level-2" data-toggle="collapse" data-parent="#level-1">Level one</a>
                <ul id="first-level-2" class="sidebar-group-secondary collapse show">
                    <li class="card">
                        <a class="collapsed" href="#first-level-3" data-toggle="collapse" data-parent="#first-level-2">Level two</a>
                        <ul id="first-level-3" class="sidebar-group-items collapse">
                            <li>
                                <a class="active" href="#">Level three</a>
                            </li>
                            <li>
                                <a href="#">Level three</a>
                            </li>
                        </ul>
                    </li>
                    <li class="card">
                        <a class="collapsed" href="#second-level-3" data-toggle="collapse" data-parent="#first-level-2">Level two</a>
                        <ul id="second-level-3" class="sidebar-group-items collapse">
                            <li>
                                <a href="#">Level three</a>
                            </li>
                            <li>
                                <a href="#">Level three</a>
                            </li>
                        </ul>
                    </li>
                </ul>
            </li>
            <li class="card">
                <a class="collapsed" href="#second-level-2" data-toggle="collapse" data-parent="#level-1">Level one</a>
                <ul id="second-level-2" class="sidebar-group-items collapse">
                    <li>
                        <a href="#">Level two</a>
                    </li>
                    <li>
                        <a href="#">Level two</a>
                    </li>
                </ul>
            </li>
        </ul>
    </nav>
</div>