Hi Herbert,
I checked your site and see that the HTML code of side menu is different than Main Menu. In order to create a side menu with similar design as Main menu, you will have to create a Custom HTML module, manual copy HTML code from Main Menu and paste there. For example, the HTML code might look like this :
<ul class="mega-nav level1">
<li data-xicon="fa fa-pencil" data-level="2" data-id="106" class="">
<a data-target="#" href="/web-design.html" class=""><i class="fa fa-pencil"></i>Web Design</a>
</li>
<li data-xicon="fa fa-google" data-level="2" data-id="108" class="">
<a data-target="#" href="/seo.html" class=""><i class="fa fa-google"></i>SEO</a>
</li>
<li data-xicon="fa fa-envelope" data-level="2" data-id="110" class="">
<a data-target="#" href="/email-marketing.html" class=""><i class="fa fa-envelope"></i>Email Marketing</a>
</li>
<li data-xicon="fa fa-globe" data-level="2" data-id="114" class="">
<a data-target="#" href="/dominios.html" class=""><i class="fa fa-globe"></i>Domínios</a>
</li>
<li data-xicon="fa fa-dollar" data-level="2" data-id="116" class="">
<a data-target="#" href="/monetizacao.html" class=""><i class="fa fa-dollar"></i>Monetização</a>
</li>
<li data-xicon="fa fa-comment-o" data-level="2" data-id="118">
<a data-target="#" href="/divulgacao.html" class=""><i class="fa fa-comment-o"></i>Divulgação</a>
</li>
</ul>