用动画不停改变背景图片位置;
动画高为无限循环;
在页面放三个DIV，首先将他们大小铺满整个窗口，这点是通过将其position设为absolute然后分别设置上左下右四个方面距离为0px达到的。
<!doctype html>
<html>
<head>
<title>Moving stars</title>
<style type="text/css">
html,body{
margin: 0;
}
.wall{
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
}
p#background{
background: black url('img/background.png') repeat-x 5% 0%;
}
p#midground{
background:url('img/midground.png')repeat 20% 0%;
z-index: 1;
}
p#foreground{
background:url('img/foreground.png')repeat 35% 0%;
z-index: 2;
}
</style>
</head>
<body>
<p id="background" class="wall"></p>
<p id="midground" class="wall"></p>
<p id="foreground" class="wall"></p>
</body>
</html>
然后定义的们的动画，让背景图片的位置从开始的0%变化到600%，注意我们只改变x方向的位置，y保持0%不变，因为我们想要的效果是水平移动，所以y方向无变化。
@-webkit-keyframes STAR-MOVE {
from {
background-position:0% 0%
}
to {
background-position: 600% 0%
}
}
@keyframes STAR-MOVE {
from {
background-position: 0% 0%
}
to {
background-position: 600% 0%
}
}
最后一步便是将动画关键帧应用到三个充当背景的DIV上。
p#background {
background: black url('img/background.png') repeat-x 5% 0%;
-webkit-animation: STAR-MOVE 200s linear infinite;
-moz-animation: STAR-MOVE 200s linear infinite;
-ms-animation: STAR-MOVE 200s linear infinite;
animation: STAR-MOVE 200s linear infinite;
}
p#midground {
background: url('img/midground.png')repeat 20% 0%;
z-index: 1;
-webkit-animation: STAR-MOVE 100s linear infinite;
-moz-animation: STAR-MOVE 100s linear infinite;
-ms-animation: STAR-MOVE 100s linear infinite;
animation: STAR-MOVE 100s linear infinite;
}
p#foreground {
background: url('img/foreground.png')repeat 35% 0%;
z-index: 2;
-webkit-animation: STAR-MOVE 50s linear infinite;
-moz-animation: STAR-MOVE 50s linear infinite;
-ms-animation: STAR-MOVE 50s linear infinite;
animation: STAR-MOVE 50s linear infinite;
}
飘动的浮云
如果把上面的星星图片换成云彩，那就成了飘动的浮云了。
代码需要小的改动，就是背景层需要设置background-size为cover，这样才能让蓝天铺满窗口。
p#background {
background: black url('img/background.png') repeat-x 5% 0%;
background-size: cover;
-webkit-animation: STAR-MOVE 200s linear infinite;
-moz-animation: STAR-MOVE 200s linear infinite;
-ms-animation: STAR-MOVE 200s linear infinite;
animation: STAR-MOVE 200s linear infinite;
}
