Kentico CSS List Menu styling

Kentico CSS List Menu styling

I am to implement this structure with kentico
<li class="megamenu_button"><a href="#_">Mega Menu</a></li>
<li><a href="#">Home</a></li>
<li class="aa"><a href="#_" class="megamenu_drop">About Us</a><!--
Begin Item -->
<div class="dropdown_4columns dropdown_container"><!-- Begin
Item Container -->
<div class="col_12">
<img class="img_left" src="images/about_us_img.png"
width="125" height="146">
<ul class="list_unstyled">
<li><a href="#_">FreelanceSwitch</a></li>
<li><a href="#_">Creattica</a></li>
<li><a href="#_">WorkAwesome</a></li>
<li><a href="#_">Mac Apps</a></li>
</ul>
</div>
</div><!-- End Item Container -->
</li><!-- End Item -->
</ul><!-- End Mega Menu -->
The design is meant to have at least 6 menu headers with sub-menu each.
The challenge is I don't even know how to approach the design. I am
currently using aspx master template. All suggestion is welcome.