How to Add an Arrow in Bootstrap Dropdown or in Simple Bootstrap Menu

Today you will learn how to add an arrow in boostrap menu because Twitter bootstrap has no class to an arrow in activated tab or page in menu. So i have written a simple class for all of you to putt an arrow in your bootstrap menu.

This is simple class just copy and paste in your custom class.
#main_menu.navbar-default .navbar-nav > .active > a:after {
content: "";
position: absolute;
bottom: -10px;
left: 45%;
border-width: 0px 5px 5px;
border-style: solid;
border-color: #c32033 transparent;
display: block;
width: 0;
}