CSS - adding another elements on hover state

All,

I have a horizontal menu bar. When the user hovers over each link in the menu bar, I want to show a small triangle underneath the link.

This small triangle is not an image but is rendered by CSS border syntax. Image and code below:

Here is the CSS code for the triangle:

#css_arrow {
    border-color: transparent transparent rgba(111,46,11,0.0) transparent;
    border-style: solid;
    border-width: 8px;
    height: 0;
    width: 0;
    position: absolute;
    top: 34px;
    left: 78px;

I want to add the triangle to the menu item in hover state.

Can someone please advise how to go about adding this id to the hover state. I thought about using two classes for the items in the menu bar but its not working out. Here is the html code:

<div id="main_bar">
                <ul>
                    <li class="maintabs maintabs_tri"><a href="#">Overview</a></li><li class="maintabs maintabs_tri"><a href="#">Collar/ Neckline</a></li><li class="maintabs maintabs_tri"><a href="#">Sleeves</a>
                    <ul>
                        <li class="s_leftright"><a href="#">Left Sleeves</a></li>
                        <li class="s_leftright"><a href="#">Right Sleeves</a></li>
                    </ul></li><li class="maintabs maintabs_tri"><a href="#">Body</a></li>
                </ul>           
            </div>

And the CSS, which doesnt work:

    .maintabs_tri:hover {
    border-color: transparent transparent rgba(111,46,11,1) transparent;
    border-style: solid;
    border-width: 8px;
    position: absolute;
    height: 0;
    width: 0;
    top: 32px;
    left: 78px;
}

You are going to need to place it on all items, but only display it on hover, i.e.

<ul>
   <li>
      <a href="#">Whatever <span></span></a>
   </li>
   <li>
      <a href="#">Whatever <span></span></a>
   </li>
   <li>
      <a href="#">Whatever <span></span></a>
   </li>
</ul>

In this case, span is going to be the triangle. I'm assuming you've already styled your ul an li appropriately. So, in your css:

ul li a {
   display: block;
   width: 100px;
   height: 32px;
   float: left;
   position: relative;
}

ul li a:hover span {
  display: block;
}

ul li a span {
    display: none;
     border-color: transparent transparent rgba(111,46,11,1) transparent;
    border-style: solid;
    border-width: 8px;
    height: 0;
    width: 0;
    position: absolute;
    bottom: 0;
    left: 50%;
}

I'm nesting it within the anchor because that maximizes the clickable area.