Transitions on the display: property

Question

I'm currently designing a kind of CSS 'mega dropdown' menu - basically a normal CSS-only dropdown menu, but one that contains different types of content.

At the moment, it appears that CSS3 Transitions don't apply to the 'display' property, i.e. you can't do any sort of transition from display: none to display: block (or any combination).

Can anyone think of a way for the second-tier menu from the above example to 'fade in' when someone hovers over one of the top level menu items?

I'm aware that you can use transitions on the visibility: property, but I can't think of a way to utilise that effectively.

I've also tried using height but that just failed miserably.

I'm also aware that it's trivial to achieve this using JavaScript, but I wanted to challenge myself to use just CSS and I think I'm coming up a little short.

All and any suggestions most welcome.

Answer 1

You can get this to work the natural way you expected - using display - but you have to throttle the browser to get it to work, using either JS or as others have suggested a fancy trick with one tag inside another. I don't care for the inner tag as it further complicates CSS and dimensions, so here's the JS solution:

https://jsfiddle.net/b9chris/hweyecu4/1/

Starting with a box like:

<div class="box hidden">Lorem</div>

A hidden box. You can have it transition on click with:

function toggleTransition() {
  var el = $("div.box1");

  if (el.length) {
    el[0].className = "box";
    el.stop().css({maxWidth: 10000}).animate({maxWidth: 10001}, 2000, function() {    
        el[0].className = "box hidden";
    });
  } else {
    el = $("div.box");
    el[0].className = "box";
    el.stop().css({maxWidth: 10001}).animate({maxWidth: 10000}, 50, function() {    
        el[0].className = "box box1";
    });
  }

  return el;
}

someTag.click(toggleTransition);

The CSS is what you'd guess:

.hidden {
  display: none;
}
.box {
    width: 100px;
    height: 100px;
    background-color: blue;
    color: yellow;
    font-size: 18px;
    left: 20px;
    top: 20px;
    position: absolute;
    -webkit-transform-origin: 0 50%;
    transform-origin: 0 50%;
    -webkit-transform: scale(.2);
    transform: scale(.2);
  -webkit-transition: transform 2s;
  transition: transform 2s;
}
.box1{
    -webkit-transform: scale(1);
    transform: scale(1);
}

The key is throttling the display property. By removing the hidden class then waiting 50ms, then starting the transition via the added class, we get it to appear and then expand like we wanted, instead of it just blipping onto the screen without any animation. Similar occurs going the other way, except we wait till the animation is over before applying hidden.

Note: I'm abusing .animate(maxWidth) here to avoid setTimeout race conditions. setTimeout is quick to introduce hidden bugs when you or someone else picks up code unaware of it. .animate() can easily be killed with .stop(). I'm just using it to put a 50ms or 2000ms delay on the standard fx queue where it's easy to find/resolve by other coders building on top of this.

Answer 2

If you are using jQuery to set your classes, this will work 100%:

$(document).ready(function() {
  $('button').click(function() {
    var container = $('.container');
    
    if (!container.hasClass('active')) {
      container.addClass('show').outerWidth();
      container.addClass('active');
    }
    else {
      container.removeClass('active').one('transitionend', function() {
        container.removeClass('show');
      });
    }
  });
});

.container {
  display: none;
  opacity: 0;
  transition: opacity 0.3s ease;
}

.container.show {
  display: flex;
}
 
.container.active {
  opacity: 1;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button type="button">Toggle</button>

<div class="container">
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</div>

Of course you could just use jQuery .fadeIn() and .fadeOut() functions, but the advantage of setting classes instead is in case you want to transition to a display value other than block (as is the default with .fadeIn() and .fadeOut()).

Here I am transitioning to display flex with a nice fade effect.

Answer 3

At the time of this post all major browsers disable CSS transitions if you try to change the display property, but CSS animations still work fine so we can use them as a work-around.

Example Code:- (You can apply it to your menu accordingly) Demo

Add the following CSS to your stylesheet:-

@-webkit-keyframes fadeIn {
    from { opacity: 0; }
      to { opacity: 1; }
}  
@keyframes fadeIn {
    from { opacity: 0; }
      to { opacity: 1; }
}

Then apply the fadeIn animation to the child on parent hover:- (and of course set display: block)

.parent:hover .child {
    display: block;
    -webkit-animation: fadeIn 1s;
    animation: fadeIn 1s;
}

Answer 4

According to W3C Working Draft 19 November 2013 display is not an animatable property. Fortunately, visibility is animatable. You may chain its transition with a transition of opacity (JSFiddle):

• HTML:

  <a href="http://example.com" id="foo">Foo</a>
  <button id="hide-button">Hide</button>
  <button id="show-button">Show</button>
  

• CSS:

  #foo {
      transition-property: visibility, opacity;
      transition-duration: 0s, 1s;
  }
  
  #foo.hidden {
      opacity: 0;
      visibility: hidden;
      transition-property: opacity, visibility;
      transition-duration: 1s, 0s;
      transition-delay: 0s, 1s;
  }
  

• JavaScript for testing:

  var foo = document.getElementById('foo');
  
  document.getElementById('hide-button').onclick = function () {
      foo.className = 'hidden';
  };
  
  document.getElementById('show-button').onclick = function () {
      foo.className = '';
  };
  

Note that if you just make the link transparent, without setting visibility: hidden, then it would stay clickable.

Answer 5

Edit: display none is not being applied in this example.

@keyframes hide {
  0% {
    display: block;
    opacity: 1;
  }
  99% {
    display: block;
  }
  100% {
    display: none;
    opacity: 0;
  }
}

What's happening above is that through 99% of the animation display is set to block while the opacity fades out. In the last moment display property is set to none.

And the most important bit is to retain the last frame after the animation ends using animation-fill-mode: forwards

.hide {
   animation: hide 1s linear;
   animation-fill-mode: forwards;
}

Here are two examples: https://jsfiddle.net/qwnz9tqg/3/

Answer 6

You can simply use css visibility: hidden/visible instead of display : none/block

div {
    visibility:hidden;
    -webkit-transition: opacity 1s ease-out;
    -moz-transition: opacity 1s ease-out;
    -o-transition: opacity 1s ease-out;
    transition: opacity 1s ease-out;
    opacity: 0; 
}

parent:hover > div {
    opacity: 1;
    visibility: visible;
}