CSS Transition not working on hover

Question

I am having an issue. When I hover over the image, a dark overlay appears but CSS Transition property is not working on it.

Here is the html:

<div class="col-md-12">
    <div class="collection-category">
        <img src="http://dummyimage.com/600x400/#C1C1C1/fff" />
        <a href="#">
            <div class="overlay_wrap">
                <div class="overlay">
                    <h2 class="collection_title">Headline One</h2>
                </div>
            </div>
        </a>
    </div>
</div>

And CSS is:

.collection-category {
    display: block;
    overflow: hidden;
    margin: 10px 0;
    position: relative;
}

.collection-category img {
    width: 100%;
    max-height: 250px;
}

.collection_title {
    display: table-cell;
    vertical-align: middle;
    font-size: 28px;
}

.overlay_wrap {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;

    -moz-transition: all .2s ease-in-out;
    -webkit-transition: all .2s ease-in-out;
    -ms-transition: all .2s ease-in-out;
    -o-transition: all .2s ease-in-out;
    transition: all .2s ease-in-out;    
}
.overlay {
    display: none;
    background: rgba(2, 2, 2, 0.61);
    color: #FFF;
    text-align: center;
    -moz-transition: all .2s ease-in-out;
    -webkit-transition: all .2s ease-in-out;
    -ms-transition: all .2s ease-in-out;
    -o-transition: all .2s ease-in-out;
    transition: all .2s ease-in-out;    
}
.collection-category:hover>a>.overlay_wrap>.overlay {
    display: table;
    height: 100%;
    width: 100%;
}

Here is the JSFiddle

http://jsfiddle.net/cnbvoe32/

Any help would be highly appreciated.

thanks in advance.

Solution

It's because you can't transition from display: none to display: table.

Instead, you could transition the opacity property by setting the initial display to table along with opacity: 0 and then transitioning to opacity: 1:

Updated Example

.overlay {
  display: table;
  background: rgba(2, 2, 2, 0.61);
  color: #FFF;
  text-align: center;
  -moz-transition: all .2s ease-in-out;
  -webkit-transition: all .2s ease-in-out;
  -ms-transition: all .2s ease-in-out;
  -o-transition: all .2s ease-in-out;
  transition: all .2s ease-in-out;
  opacity: 0;
  height: 100%;
  width: 100%;
}
.collection-category:hover>a>.overlay_wrap>.overlay {
  opacity: 1;
}