Help needed with Tabs and Sub Tabs Creation

Hi Everyone,
I'm new to Web site Page Design Just learning I have Web site https://www.fashionfore.com
This is an HTML Bootstrap Css Corrections for to alter the Tabs or Menu Font size and to Add Drop down Menu in the Skill Development Menu
<li class="nav-item-child active margin dropdown ">
<a class="nav-link dropdown-toggle" href="#" id="dropdown-a" data-toggle="dropdown">Skill Development</a>
<div class="dropdown-menu"…

Help needed with Tabs and Sub Tabs Creation