CSS animation keyframes with display none works to fade in, but not fade out

Question

I have an element which has display none on start. When i add a class to it i want it to fade in, using CSS.

I found this tutorial to use keyframes which is working nice

Answer 1

Trying to animate the display:none is the root of your problem. The confusion for why the fade-in works and the fade-out doesn't comes from the combination of using both display and opacity.

The display property is only being dictated by whether .active is applied; the animations aren't actually changing it, whereas the opacity is animated as expected. On the fade-in, this means that you immediately show your element, which then transitions from transparent to opaque. On the fade-out, this means that you immediately hide your element, which then transitions from opaque to transparent while hidden.

There are a couple different ways you could solve this, but it sort of depends on the context. For example, you could leave it as a block element and use the height property to make it collapse:

$('button').on('click', function(e) {
  e.preventDefault();
  $(this).siblings('.box').toggleClass('active');
})

@import "bourbon";
 * {
  box-sizing: border-box;
  text-align: center;
}
button {
  margin: 30px 0;
  border: 1px solid #ccc;
  text-align: center;
  padding: 1em;
  background: none;
  box-shadow: none;
}
.box {
  margin: 0 auto;
  width: 80%;
  height: 0;
  display: block;
  line-height: 100px;
  background: #ccc;
  border: 1px solid #444;
  text-align: center;
  opacity: 0;
  animation: FadeOut 1s ease-in-out;
}
.box.active {
  display: block;
  height: initial;
  opacity: 1;
  animation: FadeIn 1s ease-in-out;
}
@keyframes FadeIn {
  0% {
    opacity: 0;
    height: initial;
  }
  100% {
    opacity: 1;
    height: initial;
  }
}
@keyframes FadeOut {
  0% {
    opacity: 1;
    height: initial;
  }
  99% {
    opacity: 0;
    height: initial;
  }
  100% {
    height: 0;
    opacity: 0;
    height: 0;
  }
}

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Extra paragraph to show collapse