Question

Sorry I can’t put this code live anywhere at the moment but hopefully the screenshots will help. I’m trying to precisely center a sub-menu ul beneath li’s of variable width, like so:

Here’s a truncated version of my layout:

<div class="nav">
  <ul class="menu">
     <li>
          <a href="">Home</a>  
     </li>
     <li>
          <a href="">Kids</a>
          <ul class="sub-menu">
              <li><a href="">Sub-item 1</a></li>
              <li><a href="">Sub-item 2</a></li>
          </ul>
     </li>
     <li>
          <a href="">Students</a>  
     </li>        
     <li>
          <a href="">Adults</a>
          <ul class="sub-menu">
              <li><a href="">Sub-item 1</a></li>
              <li><a href="">Sub-item 2</a></li>
          </ul
     </li>
  </ul>
</div>

I have the arrow on the sub-menu working and aligned to the center of the sub-menu ul, but the sub-menu itself isn’t aligning correctly with its parent li, as you can see here. The sub-menus showing are for the “kids” li and the “adults” li, as above:

This is the relevant code, I believe. Any help is MUCH appreciated!

.menu li {
    display:inline-block;
    list-style-type: none;
    position: relative;
}

.menu li a {
    background:url("_/images/nav-cross-home.png") 50% 5px no-repeat;
    display:inline-block;
    padding:30px 5px 2px;
    text-transform: uppercase;
    text-decoration: none;
    color:#000;
    font-family:proxima-nova, Arial, Helvetica, sans-serif;
    font-weight:700;
    font-size:.9em;
    margin: 0 auto 10px;
}
.nav ul ul {
    display: block;
    position: absolute;
    margin: 10px 0px 0px -15px;
    top: 3.333em;
    left: -125%;
    width: 170px;
    z-index: 99999;
    border:2px solid #929292;
}

.nav ul.menu ul.sub-menu a {
    background: #fff !important;
    border-bottom: 1px solid #e5e5e5;
    color: #444;
    font-size: .9em;
    text-transform: none;
    height: auto;
    line-height: 1.4em;
    padding: 10px 10px;
    width: 150px;
    margin-bottom:0px;
}

Answer 1

Here you go.

.nav ul ul {
    margin-left:-87px;
    left: 50%;
}

So left 50% gets the ul to the mid point of the parent li, and then negative left margin half of the total width (including borders = 174).

Update: here’s an example. http://jsfiddle.net/mcpatriot/jzWcD/