CSS3 Transition，悬停以触发子元素无法正常工作的动画

Question

I would like my list item to trigger a css3 transition on its child item .pusher when hovered over. I am used to doing this in JS and not css3 transitions, after reading some other SO questions I thought I understood how to do it, but it's not working correctly:

#sidebar ul {
    float: left;
    list-style: none;
    padding: 0;
    margin: 0;
    width: 100%;
}
#sidebar ul li {
    padding: 20px;
    position: relative;
    list-style: none;
    border-bottom: 1px solid #4a4a4a;
    cursor: pointer;
    -webkit-transition: max-width 0.5s ease;
    transition: max-width 0.5s ease;
}
#sidebar ul li a {
    color: #fff;
    z-index: 5;
    position: relative;
}
#sidebar ul li a:hover {
    text-decoration: none;
}
#sidebar ul li:hover > .pusher {
    max-width: 100px;
    height: 100%;
    background: #383838;
    position: absolute;
    left: 0;
    top: 0;
    z-index: 1;
}
#sidebar ul li:first-child {
    border-top: 1px solid #4a4a4a;
}

Pusher is actually being appended to li, with JS, but I don't think this should cause an issue? (edit: this does not appear to be the issue)

fiddle: http://jsfiddle.net/8KpQW/

Answer 1

You haven't defined a width for .pusher merely a max-width so it doesn't know how wide it is supposed to be.

Try this

JSFiddle Demo

CSS extract

.pusher {
    width:0;
    transition:width 0.5s ease;
}

#sidebar ul li:hover .pusher {
    width: 100px;
    height: 100%;
    background: #383838;
    position: absolute;
    left: 0;
    top: 0;
    z-index: 1;
}

Answer 2

The code below fixed the issue for me :

 #sidebar {
  height: 100%;
  margin-top: 74px;
  background: #303030;
  color: #fff;
}
#sidebar ul {
  float: left;
  list-style: none;
  padding: 0;
  margin: 0;
  width: 100%;
}
#sidebar ul li {
  padding: 20px;
  position: relative;
  list-style: none;
  border-bottom: 1px solid #4a4a4a;
  cursor: pointer;
}
#sidebar ul li a {
  color: #fff;
  z-index: 5;
  position: relative;
}
#sidebar ul li a:hover {
  text-decoration: none;
}
#sidebar ul li .pusher {
  height: 100%;
  width: 0px;
  background: #383838;
  position: absolute;
  left: 0;
  top: 0;
  z-index: 1;
  -webkit-transition: width 0.2s ease-in-out;
  -moz-transition: width 0.2s ease-in-out;
  -o-transition: width 0.2s ease-in-out;
  transition: width 0.2s ease-in-out;
}
#sidebar ul li:hover > .pusher {
  width: 100%;
}

the transition property needs to be applied to the actual element to be animated, not the hover trigger element. hover, merely needs to contain the property value that the animation will end on.

fiddle: http://jsfiddle.net/8KpQW/3/