'Ello Stackoverflow!

I'm wondering if anyone could help me figuring this out.
I found [this](http://codepen.io/jasonmayes/pen/hzvLd/) Before/After image viewer by Jason Mayes and I was working on getting it to be responsively centered.

So I found "object-fit: cover;" and "object-position: 50% 50%;" to work great but I soon realised that the transition itself was not being styled that way, somehow.

I forked Jason's pen to show you more clearly:
<http://codepen.io/RogerAntonio/pen/rVXrma>

I think the problem lies here somewhere:

```
.container img {
  object-fit: cover;
  object-position: 50% 50%;
  overflow: hidden;
}

.beforeAfter .before {
  z-index:2;
  opacity: 1;
  -webkit-transition: opacity 1s ease-in-out;
  -moz-transition: opacity 1s ease-in-out;
  -ms-transition: opacity 1s ease-in-out;
  -o-transition: opacity 1s ease-in-out;
  transition: opacity 1s ease-in-out;
}

```

Thank you in advance!