Can I apply a CSS transition on hover-out only?

Question

The CSS transition property lets you animate on both hover-in & hover-out if you put the transition as below:

#inner{
    opacity:0;
    transition:opacity 2000ms;
}
#outer:hover #inner{
    opacity:1;
}

However, if the transition is moved to :hover state, it only happens on hover-in.

#inner{
    opacity:0;
}
#outer:hover #inner{
    opacity:1;
    transition:opacity 2000ms;
}

Is it possible to do the reverse, i.e. animate on hover-out only?

Answer 1

Here's one way to achieve this (put a bogus property none for transition property in :hover):

#inner2{
    opacity:0;
    transition:opacity 2000ms;
}
#outer:hover #inner2{
    opacity:1;
    transition:none;
}

http://jsfiddle.net/j716sbav/4/

Answer updated to incorporate @BoltClock's suggestion. Putting none instead of a bogus property is definitely more elegant.

Answer 2

I know this is a very old post but, as it came up in response to my Google search on the subject, I thought I'd post my solution.

After reading everything posted here, I found the simplest solution. Place a transition on the initial state as follows:

.btn {
  opacity:0;
  transition:0.6s;
}

.btn:hover {
  opacity:1;
  transition:0.8s;
}

So it has a transition time to the hover state and a transition time to the non-hover (ie normal) state. Saves a whole bunch of code.