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

I ran into this today, with a position: fixed modal that I was reusing. I couldn't keep it display: none and then animate it, as it just jumped into appearance, and and z-index (negative values, etc) did weird things as well.

I was also using a height: 0 to height: 100%, but it only worked when the modal appeared. This is the same as if you used left: -100% or something.

Then it struck me that there was a simple answer. Et voila:

First, your hidden modal. Notice the height is 0, and check out the height declaration in transitions... it has a 500ms, which is longer than my opacity transition. Remember, this affects the out-going fade-out transition: returning the modal to its default state.

#modal-overlay {
    background: #999;
    background: rgba(33,33,33,.2);
    display: block;
    overflow: hidden;
    height: 0;
    width: 100%;
    position: fixed;
    top: 0;
    left: 0;
    opacity: 0;
    z-index: 1;
    -webkit-transition: height 0s 500ms, opacity 300ms ease-in-out;
       -moz-transition: height 0s 500ms, opacity 300ms ease-in-out;
            -ms-transition: height 0s 500ms, opacity 300ms ease-in-out;
         -o-transition: height 0s 500ms, opacity 300ms ease-in-out;
        transition: height 0s 500ms, opacity 300ms ease-in-out;
}

Second, your visible modal. Say you're setting a .modal-active to the body. Now the height is 100%, and my transition has also changed. I want the height to be instantly changed, and the opacity to take 300ms.

.modal-active #modal-overlay {
    height: 100%;
    opacity: 1;
    z-index: 90000;
    -webkit-transition: height 0s, opacity 300ms ease-in-out;
       -moz-transition: height 0s, opacity 300ms ease-in-out;
        -ms-transition: height 0s, opacity 300ms ease-in-out;
         -o-transition: height 0s, opacity 300ms ease-in-out;
            transition: height 0s, opacity 300ms ease-in-out;
}

That's it, it works like a charm.

Answer 2

I suspect anyone just starting CSS transitions quickly discovers that they don't work if you're modifying the display property (block/none) at the same time. One work-around that hasn't yet been mentioned is that you can continue to use display:block/none to hide/show the element, but set its opacity to 0 so that even when it's display:block, it's still invisible. Then to fade it in, add another CSS class such as "on" which sets the opacity to 1 and defines the transition for opacity. As you may have imagined, you'll have to use JavaScript to add that "on" class to the element, but at least you're still using CSS for the actual transition.

P.S. If you find yourself in a situation where you need to do both display:block, and add class "on", at the same time, defer the latter using setTimeout. Otherwise the browser just sees both things as happening at once and disables the transition.

Answer 3

you can also use this:

.dropdown {
height: 0px;
width: 0px;
opacity: .0;
color: white;
}
.dropdown:hover {
height: 20px;
width: 50px;
opacity: 1;
transition: opacity 200ms;
/* Safari */
-webkit-transition: opacity 200ms;
}

Answer 4

Change overflow:hidden to overflow:visible. It works better. I use like this:

#menu ul li ul {
    background-color:#fe1c1c;
    width:85px;
    height:0px;
    opacity:0;
    box-shadow:1px 3px 10px #000000;
    border-radius:3px;
    z-index:1;
    -webkit-transition:all 0.5s ease;
    -moz-transition:all 0.6s ease;
}

#menu ul li:hover ul  {
    overflow:visible;
    opacity:1;
    height:140px;
}

visible is better because overflow:hidden act exactly like a display:none.

Answer 5

It can be handle by using transition timing functions step-end and step-start

For example: https://jsfiddle.net/y72h8Lky/

$(".run").on("click", function() {
    $(".popup").addClass("show");
});
$(".popup").on("click", function() {
    $(".popup").removeClass("show");
})

.popup {
    opacity: 0;
    display: block;
    position: absolute;
    top: 100%;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 1450;
    background-color: rgba(0, 175, 236, 0.6);
    transition: opacity 0.3s ease-out, top 0.3s step-end;
}
.popup.show {
    transition: opacity 0.3s ease-out, top 0.3s step-start;
    opacity: 1;
    top: 0;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="popup"></div>
<button class="run" style="font-size: 24px;">Click on me</button>

Answer 6

I started an open source skeleton project called Toggle Display Animate

https://marcnewton.github.io/Toggle-Display-Animate/

This skeleton helper will allow you to easily mimic jQuery show/hide but with in/out CSS3 transition animations.

It uses class toggles so you can use any css methods you want on elements besides display:none|block|table|inline etc as well as other alternate uses that can be thought up.

Its main design purpose is for element toggle states, it supports a revert state where hiding the object allows you to run your keyframe in reverse or play an alternate animation for hiding the element.

Most of the markup for the concept I am working on is CSS, there is very little javascript actually used.

There is a demo here: http://marcnewton.co.uk/projects/toggle-display-animate/