html - CSS3 transition doesn't work with display property

I have been trying to use css to show a Hidden Div fade in whenever I hover its parent element.

So far all I have managed to do was to get the hidden div to show, but there are no easing transitions what so ever.

Here is my Code on JSfiddle http://jsfiddle.net/9dsGP/

Here is my Code:

HTML:

This is a Button
    

    This is the Hidden Div
    

CSS:

#header #button {width:200px; background:#eee}

#header #button:hover > .content {display:block; opacity:1;}

#header #button .content:hover { display:block;}

#header #button .content {

-webkit-transition: all .3s ease .15s;
-moz-transition: all .3s ease .15s;

-o-transition: all .3s ease .15s;
-ms-transition: all .3s ease .15s;
transition: all .3s ease .15s;

    opacity:0;
    clear: both;
    display: none;

    top: -1px;
    left:-160px;

    padding: 8px;
    min-height: 150px;
    border-top: 1px solid #EEEEEE;
    border-left: 1px solid #EEEEEE;
    border-right: 1px solid #EEEEEE;
    border-bottom: 1px solid #EEEEEE;
    -webkit-border-radius: 0px 7px 7px 7px;
    -moz-border-radius: 0px 7px 7px 7px;
    -khtml-border-radius: 0px 7px 7px 7px;
    border-radius: 0px 7px 7px 7px;

    -webkit-box-shadow: 0px 2px 2px #DDDDDD;
    -moz-box-shadow: 0px 2px 2px #DDDDDD;
    box-shadow: 0px 2px 2px #DDDDDD;
    background: #FFF;
}

Any clue as to what Im doing wrong? Just trying to get a smooth effect for the hidden content when I hover over the button. Thanks in advance!

Answer

display:none; removes a block from the page as if it were never there.
A block cannot be partially displayed; it’s either there or it’s not.
The same is true for visibility; you can’t expect a block to be half
hidden which, by definition, would be visible! Fortunately, you can
use opacity for fading effects instead.
- reference

As an alternatiive CSS solution, you could play with opacity, height and padding properties to achieve the desirable effect:

#header #button:hover > .content {

    opacity:1;
    height: 150px;
    padding: 8px;    
}

#header #button .content {
    opacity:0;
    height: 0;
    padding: 0 8px;
    overflow: hidden;

    transition: all .3s ease .15s;
}

(Vendor prefixes omitted due to brevity.)

Here is a working demo. Also here is a similar topic on SO.

#header #button {
  width:200px;
  background:#ddd;
  transition: border-radius .3s ease .15s;
}

#header #button:hover, #header #button > .content {
    border-radius: 0px 0px 7px 7px;
}


#header #button:hover > .content {
  opacity: 1;
  height: 150px;
  padding: 8px;    
}

#header #button > .content {
  opacity:0;
  clear: both;
  height: 0;

  padding: 0 8px;
  overflow: hidden;

  -webkit-transition: all .3s ease .15s;
  -moz-transition: all .3s ease .15s;
  -o-transition: all .3s ease .15s;
  -ms-transition: all .3s ease .15s;
  transition: all .3s ease .15s;

  border: 1px solid #ddd;


  -webkit-box-shadow: 0px 2px 2px #ddd;
  -moz-box-shadow: 0px 2px 2px #ddd;
  box-shadow: 0px 2px 2px #ddd;
  background: #FFF;
}

#button > span { display: inline-block; padding: .5em 1em }

  
 This is a Button

    

      This is the Hidden Div