How to fade in background image by CSS3 Animation

问题

I am making a menu that each item has a text like item1, item2 and etc. in hover the background colour changes, text becomes transparent and a background image replaces. I used this code to ease in and out the style. but it only works for background colour and not the image.

#nav li:hover {
    color:transparent !important;
    text-shadow: none;
    background-color: rgba(255, 0, 0, .5);

    -webkit-transition: all 1s ease-in;
    -moz-transition: all 1s ease-in;
    -o-transition: all 1s ease-in;
    -ms-transition: all 1s ease-in;
    transition: all 1s ease-in;
}

Here is the online version: http://jsfiddle.net/q4uHz/

回答1:

Background images cannot be animated; there would be no algorithm for that. A simple solution is to include <img> with the icon in your HTML instead with opacity: 0 and animate that. Something like.

<li id="home">
<img src="http://cdn3.iconfinder.com/data/icons/picons-social/57/16-apple-48.png">
<a href="#home">Home</a></li>

#nav li {
    position: relative;
}
#nav li img {
    opacity: 0;
    position: absolute;
    transition: all 1s ease-in;
    top: 0;
    left: 0;
}
#nav li:hover img {
    opacity: 1;
}

http://jsfiddle.net/ExplosionPIlls/q4uHz/1/

来源：https://stackoverflow.com/questions/16905621/how-to-fade-in-background-image-by-css3-animation