How to make CSS Dropdown menu slidedown

Question

I created a CSS menu with dropdown and I hide the sub menu and display it when you hover over the menu item and I was wondering if it is possible with CSS with some type of CSS transition to make it instead slide down. You cake take a look at a mock up of the menu here.

#main-nav {
  position: relative;
}

#main-nav>ul>li {
  width: 12.5%;
  float: left;
  text-align: center;
  line-height: .9em;
  font-weight: bold;
  background: #ccc;
}

#main-nav>ul>li>a {
  display: block;
  color: #333;
  line-height: 12px;
  font-size: 14px;
  padding: 22px 0;
  text-decoration: none;
}

.nav-dropdown {
  margin: -5px auto;
  position: absolute;
  left: -999em;
  /* Hides the drop down */
  text-align: left;
  padding: 0;
  border-top: 0;
  width: 500px;
  background: #333;
  color: #f2f2f2;
  border-bottom: 10px solid #25272a;
  -webkit-border-bottom-right-radius: 5px;
  -webkit-border-bottom-left-radius: 5px;
  -moz-border-radius-bottomright: 5px;
  -moz-border-radius-bottomleft: 5px;
  border-bottom-right-radius: 5px;
  border-bottom-left-radius: 5px;
}

#main-nav li:hover .nav-dropdown {
  left: 0;
  top: auto;
  z-index: 11;
}

<div id="main-nav">
  <ul>
    <li><a href="#">Item 1</a></li>
    <li><a href="#">Item 2</a></li>
    <li><a href="#">Item 3</a>
      <!-- Start Blog Drop Down-->
      <div class="nav-dropdown">
        <p>have this item slide down from CSS</p>
      </div>
      <!-- /.nav-dropdown -->
    </li>
  </ul>
</div>

Solution

Yes you can, but you need to use the max-height property as described here or you can just use a fixed height as described in the previous answer.

CSS

.nav-dropdown {
    margin: 0 auto;  
    height: 0; /* Hides the drop down */ 
    overflow: hidden;
    text-align:left;  
    padding: 0;  
    border-top: 0;
    width: 500px;
    background:#333;
    color: #f2f2f2;
    -webkit-border-bottom-right-radius: 5px;
    -webkit-border-bottom-left-radius: 5px;
    -moz-border-radius-bottomright: 5px;
    -moz-border-radius-bottomleft: 5px;
    border-bottom-right-radius: 5px;
    border-bottom-left-radius: 5px;
    border-bottom: 0;
    max-height:0px;
}

#main-nav li:hover .nav-dropdown {
    height:auto;
    z-index: 11; 
    max-height:200px;
    transition-property: all;
    transition-duration: 1s;
    border-bottom: 10px solid #25272a;
}

http://jsfiddle.net/L8WVP/7/

This might also be of your interest.

Comments

[Greenhoe]

thanks, but if you take a look it in effect with a mega drop down that is dynamic based off wordpress posts I'm having a little issue as the content shows up while it slides in. you can take a look at hearthable.com and see the issue i"m talking about.

[Greenhoe]

Yea, that is the issue I'm having where the background is sliding down but the content isn't so it just looks a bit odd