How to add items to a dropdown menu

[duende.]

Regards.

I want to add a dropdown menu in the Welcome block and add this items

{Avatar} Bienvenido User -> CP Usuario
                                        -> Panel de moderación
                                        -> Panel de moderación
                                        -> Panel de administración
                                        -> Cerrar Sesión


I have this code:

Code:

<div  class="collapse navbar-collapse">
        <ul class="nav navbar-nav">
            <li class="dropdown-menu"><a href="{$mybb->settings['bburl']}/member.php?action=profile&uid={$mybb->user['uid']}">{$mybb->user['username']}</a>
                <ul>
                    <li><a href="{$mybb->settings['bburl']}/usercp.php"><i class="fa fa-filter" style="color: #b0d4e3;"></i>Panel Usuario</a></li>
                    {$modcplink}
                    {$admincplink}
                <div  class="collapse navbar-collapse">
        <ul class="nav navbar-nav">
            <li class="dropdown-menu"><a href="{$mybb->settings['bburl']}/member.php?action=profile&uid={$mybb->user['uid']}">{$mybb->user['username']}</a>
                <ul>
                    <li><a href="{$mybb->settings['bburl']}/usercp.php"><i class="fa fa-filter" style="color: #b0d4e3;"></i>Panel Usuario</a></li>
                    {$modcplink}
                    {$admincplink}
                    <li><a href="{$mybb->settings['bburl']}/member.php?action=logout&amp;logoutkey={$mybb->user['logoutkey']}"><i class="fa fa-power-off"  style="color: #c1eca5;"></i> Cerrar Sesión</a></li>
                </ul>
            </li>
        </ul>
    </div>

Am I on the right way?.

How I could to add CSS without damage theme?

My website is: https://www.forodinero.net

Thanks for your help