CSS dropdown menu transition

Question

I am trying to add dropdown transition for the menu I am working on, but it seems that I have no idea what I am doing wrong. The menu itself appears instantly, ignorning the transition effect.

CSS code I use for transition:

-webkit-transition: height 0.3s ease-in;
-moz-transition: height 0.3s ease-in;
-o-transition: height 0.3s ease-in;
-ms-transition: height 0.3s ease-in;
transition: height 0.3s ease-in;
opacity:0;

As far as I know I should add it to the nav ul ul CSS block, and adding opacity:1 to nav ul li:hover > ul but it does not work.

And here's whole code of the menu.

HTML

<nav>
    <ul>
        <li><a href="http://www.www.com/">Menu 1</a></li>
        <li><a href="http://www.www.com/">Menu 2</a></li>
        <li><a>Dropdown Here</a>
            <ul>
                <li><a href="http://www.www.com/">Dropdown1</a></li>
                <li><a href="http://www.www.com/">Dropdown2</a></li>
                <li><a href="http://www.www.com/">Dropdown3</a></li>
            </ul>
        </li>
        <li><a href="http://www.www.com/">Menu 4</a></li>
        <li><a href="http://www.www.com/">Menu 5</a></li>
    </ul>
</nav>

And the CSS I am using

nav ul {
    background: #efefef; 
    background: linear-gradient(top, #efefef 0%, #bbbbbb 100%);  
    background: -moz-linear-gradient(top, #efefef 0%, #bbbbbb 100%); 
    background: -webkit-linear-gradient(top, #efefef 0%,#bbbbbb 100%); 
    box-shadow: 0px 0px 9px rgba(0,0,0,0.15);
    padding: 0 25px;
    border-radius: 10px;  
    list-style: none;
    position: relative;
    display: inline-table;
    float:right;
    z-index:9999;

}

nav ul ul {
    display: none;
    -webkit-transition: height 0.3s ease-in;
    -moz-transition: height 0.3s ease-in;
    -o-transition: height 0.3s ease-in;
    -ms-transition: height 0.3s ease-in;
    transition: height 0.3s ease-in;
    opacity:0;      
}

nav ul li:hover > ul {
    display: block;
    opacity:1;
}

nav ul:after {
    content: ""; 
    clear: both; 
    display: block;
}

nav ul li {
    float: left;
}

nav ul li:hover {
    background: #4b545f;
    background: linear-gradient(top, #4f5964 0%, #5f6975 40%);
    background: -moz-linear-gradient(top, #4f5964 0%, #5f6975 40%);
    background: -webkit-linear-gradient(top, #4f5964 0%,#5f6975 40%);
}

nav ul li:hover a {
    color: #fff;
}

nav ul li a {
    display: block;
    padding: 30px 20px;
    color: #757575; 
    text-decoration: none;
}

nav ul ul {
    background: #5f6975; 
    border-radius: 0px; 
    padding: 0;
    position: absolute; 
    top: 100%;
}

nav ul ul li {
    float: none; 
    border-top: 1px solid #6b727c;
    border-bottom: 1px solid #575f6a; 
    position: relative;
}

nav ul ul li a {
    padding: 15px 40px;
    color: #fff;
}   

nav ul ul li a:hover {
    background: #4b545f;
}

nav ul ul ul {
    position: absolute; left: 100%; top:0;
}

Answer 1

Your transition doesn't fire, because the height of your elements isn't changed during :hover, only display and opacity. To make your elements fade in - you need to change your transition property to opacity or all.

If you want to transition height - you need to set your element height to 0, and then change it on :hover.

Be aware though - height transitions work only for specified height value, and won't work for something like height: auto;. There is a workaround for it, as follows:

ul {
    transition: all 0.5s;
    max-height: 0;
}

ul:hover {
    max-height: 200px; //or whatever could be your max-height value - don't overdo it, will be crappy transition.
}