CSS :after hover Transition

Question

The HTML structure

<div id="small_gal">
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
</div>

The images are having dropshadows so border is not a solution, as it will be outside the image

The border is having transition and it works smoothly on FF but not in chrome or other browsers

Here is the code which I have used

#small_gal div:hover{cursor: pointer;}
#small_gal div:after {
    content: '';
    position: absolute;
    width: 112px;
    height: 81px;
    border: 3px solid #e27501;
    left: 9px; top: 9px;
    z-index: 9;

    opacity: 0;
    -webkit-transition: opacity 0.5s ease-in-out;
    -moz-transition: opacity 0.5s ease-in-out;
    -o-transition: opacity 0.5s ease-in-out;
    -ms-transition: opacity 0.5s ease-in-out;
    transition: opacity 0.5s ease-in-out;
}
#small_gal div:hover:after {
    opacity: 1;
}

Note:

#small_gal

is only the container each image is wrapped in a div so we can implement :after

Answer 1

Firefox 4+ is the only browser that supports the transitioning of pseudo-elements such as :before and :after.

Source: http://css-tricks.com/13555-transitions-and-animations-on-css-generated-content/

Answer 2

CSS transitions are still experimental in WebKit so it's likely you've hit some edge-case bug involving the ::after pseudo-selector. I suggest avoiding it altogether and just transitioning border-color instead. This worked fine in Chrome and Safari:

#small_gal div.p {
    border: 2px solid transparent;
    -webkit-transition: border-color 1s ease-in;
}

#small_gal div.p:hover {
    border-color: orange;
}

Answer 3

You can use CSS transitions on pseudo elements like :before and :after if you can define the property on the element itself and use inherit in the pseudo element. So in your case instead of putting a transition on the opacity, you could put a transition on the border-color.

*, *:before, *:after {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

#small_gal div {
  border-color: transparent;
  cursor: pointer;
  display: inline-block;
  position: relative;
  -webkit-transition: border-color 0.5s ease-in-out;
  -moz-transition: border-color 0.5s ease-in-out;
  -o-transition: border-color 0.5s ease-in-out;
  -ms-transition: border-color 0.5s ease-in-out;
  transition: border-color 0.5s ease-in-out;
}
#small_gal div:after {
  content: '';
  position: absolute;
  width: 100%;
  height: 100%;
  border-color: inherit;
  border-style: solid;
  border-width: 3px;
  left: 0;
  top: 0;
}
#small_gal div:hover {
  border-color: #e27501;
}
#small_gal div img {
  display: block;
  height: auto;
  max-width: 150px;
  width: auto;
}

<div id="small_gal">
    <div><img src="//c2.staticflickr.com/6/5826/23633880170_4bb8492de8_z.jpg" /></div>
    <div><img src="//c2.staticflickr.com/6/5826/23633880170_4bb8492de8_z.jpg" /></div>
    <div><img src="//c2.staticflickr.com/6/5826/23633880170_4bb8492de8_z.jpg" /></div>
    <div><img src="//c2.staticflickr.com/6/5826/23633880170_4bb8492de8_z.jpg" /></div>
    <div><img src="//c2.staticflickr.com/6/5826/23633880170_4bb8492de8_z.jpg" /></div>
</div>