css有个执行简单动画的写法，比如animation。
我给你个例子：
#head-pic,#head-pic2{
width:145pxheight:145pxposition:absolute
top:200px
left:68px
z-index:2
border-radius:100px
-webkit-border-radius:100px
-moz-border-radius:100px
border:3px solid #fff
}
/*为浏览器兼容设置*/
@keyframes headpic-slider{
from{background:url(../images/head-pic.jpg)opacity:1.0}
to{background:url(../images/head-pic.jpg)opacity:0}
}
@keyframes headpic-slider2{
from{background:url(../images/head-pic2.jpg)opacity:0}
to{background:url(../images/head-pic2.jpg)opacity:1.0}
}
@-moz-keyframes headpic-slider{
from{background:url(../images/head-pic.jpg)opacity:1.0}
to{background:url(../images/head-pic.jpg)opacity:0}
}
@-moz-keyframes headpic-slider2{
from{background:url(../images/head-pic2.jpg)opacity:0}
to{background:url(../images/head-pic.jpg)opacity:1.0}
}
@-webkit-keyframes headpic-slider{
from{background:url(../images/head-pic.jpg)opacity:1.0}
to{background:url(../images/head-pic.jpg)opacity:0}
}
@-webkit-keyframes headpic-slider2{
from{background:url(../images/head-pic2.jpg)opacity:0}
to{background:url(../images/head-pic2.jpg)opacity:1.0}
}
@-o-keyframes headpic-slider{
from{background:url(../images/head-pic.jpg)opacity:1.0}
to{background:url(../images/head-pic.jpg)opacity:0}
}
@-o-keyframes headpic-slider2{
from{background:url(../images/head-pic2.jpg)opacity:0}
to{background:url(../images/head-pic2.jpg)opacity:1.0}
}
#head-pic{
animation:headpic-slider 20s linear infinite
-moz-animation:headpic-slider 20s linear infinite
-webkit-animation:headpic-slider 20s linear infinite
}
#head-pic2{
animation:headpic-slider2 20s linear infinite
-moz-animation:headpic-slider2 20s linear infinite
-webkit-animation:headpic-slider2 20s linear infinite
}
首先 写多个背景的class比如
.imgA {background: url(demo1.jpg) no-repeat}
.imgB {background: url(demo2.jpg) no-repeat}
....
然后在需要切换背景的层上用js替换class就行
CSS能更换的图片，只能存在于样式中。所以，这个图片也只能是背景图片。
一般是结合：hover来实现的。例如：
.mydiv{
background:图片1 no-repeat
height:100px
widht:100px
}
.mydiv:hover{
background:图片2 no-repeat
}
这样就实现了图片1和图片2的鼠标移上去的切换。
CSS层叠样式表(英文全称：Cascading Style Sheets)是一种用来表现HTML（标准通用标记语言的一个应用）或XML（标准通用标记语言的一个子集）等文件样式的计算机语言。CSS不仅可以静态地修饰网页，还可以配合各种脚本语言动态地对网页各元素进行格式化。
