CSS元素选择器

http://www.w3school.com.cn/cssref/css_selectors.asp
1.选择内嵌元素

 .demo1 .demo2{ background-color: #2F5BFF;        }

<div class="demo1">qq        <div class="demo2">222</div>    </div>

2.必须两个属性都包含

 .demo1{ width: 200px;            height: 200px;}        .demo2{ width: 100px;            height: 100px;}        .demo1.demo2{            background-color: #2F5BFF;        }

 <div class="demo1 demo2">111</div>

3，4某些标签选择器

.demo1{ width: 200px;
height: 200px;}
.demo2{ width: 100px;
height: 100px;}
.demo1> .demo2{
background-color: #2F5BFF;
}

qq

222

5.选择demo1下包含box的元素

<div class="demo1 demo2">111</div>  <div class="demo2 box">222</div>  <div class="demo2 box">333</div>

 .demo1{ width: 200px;            height: 200px;}        .demo2{ width: 100px;            height: 100px;}          .demo1~.box{            background-color: #2F5BFF;        }