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老师批语：
今天的课程：css中常用定位；伪类选择器hover；元素显示隐藏
定位：
relative:相对定位元素的定位是相对其正常位置,相对定位元素经常被用来作为绝对定位元素的容器块;
fixed:元素的位置相对于浏览器窗口是固定位置;
absolute:
绝对定位的元素的位置相对于最近的已定位父元素，如果元素没有已定位的父元素，那么它的位置相对于出始包含块
特点：绝对定位使元素的位置与文档流无关，因此不占据空间 ; 通常与相对定位连用（子绝父相）
z-index 属性设置元素的堆叠顺序 注意:Z-index 仅能在定位元素上奏效
伪选择器:hover
鼠标悬浮到元素上会触发hover
元素显示与隐藏：
display:block / none
优酷案例
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<link rel="stylesheet" href="static/font-awesome-4.7.0/css/font-awesome.min.css">
<style type="text/css">
*{margin: 0;padding: 0}
li{list-style: none;float: left}
a{text-decoration: none;color: #000;}
.clear{clear: both} /**/
.mr{margin-right: 10px;}
.l{float: left} /* 左浮动 */
a span{margin-top: 5px}
li small{margin-top: 2px;}
.conts{
width: 1740px;
margin: 0 auto;
}
.cont{width: 100%;
margin-top: 20px;
}
.cont-ul{line-height: 70px;}
.hot-tv img{width: 240px;height: 360px;}
.tab li{margin-right: 20px;}
.tv-tab img{width: 240px;height: 135px;}
.tv-tab img:hover{box-shadow: 0px 2px 20px skyblue}
.tv-show .tv-tab{margin-bottom: 15px;}
/*头部*/
.header{
position: relative;
width: 100%;
height: 520px;
background: #E8E8E8;
}
.pic-show{
width: 1740px;
height: 520px;
margin: 0 auto;
background: url("https://ykimg.alicdn.com/develop/image/2019-03-14/4be9792c38ab7f0abee4d12542e09905.jpg") no-repeat;
}
.bg{background:url("https://gw.alicdn.com/mt/TB1A4OaolTH8KJjy0FiXXcRsXXa-1664-520.png");
width: 100%;
height: 100%;
position: absolute;
top: 0;
left: 0;
z-index: 10;
}
.menu_ul{position: fixed;
top:20px;
left: 120px;
z-index: 15;
}
.menu_ul form{
width: 500px;
height: 40px;
position: relative;
left: 430px;
}
.menu_ul input{
width: 500px;height: 40px;
border-radius: 100px;
border: none;
background: rgba(234,234,234,0.5);
outline: 0;
}
.menu_ul button{
position: absolute;
top:0;
right: 0;
width: 90px;
height: 40px;
border-top-right-radius: 30px;
border-bottom-right-radius: 30px;
background: #B30702;
border: none;
color: white;
outline: 0;
}
.menu_li{position: relative;
}
</style>
</head>
<body>
<div class="header">
<div class="pic-show"></div>
<div class="bg"></div>
<div class="menu_ul">
<div class="l">
<img class="l" src="https://img.alicdn.com/tfs/TB1dw0vqHGYBuNjy0FoXXciBFXa-120-24.png">
<form action="" method="" class="l">
<input type="text" name="">
<button>全网搜</button>
</form>
</div>
<ul class="menu_li">
<li><i class="fa fa-diamond"></i></li>
</ul>
</div>
</div>
<div class="conts">
<div class="cont">
<div class="cont-ul">
<h2>正在热播</h2>
</div>
<ul class="hot-tv">
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C774CC7859B5D335803D155?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li >
<a href="">
<img src="http://r1.ykimg.com/050E00005C346D1C859B5E79630A6226?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
</ul>
<div class="clear"></div>
</div>
<div class="cont">
<div class="cont-ul">
<h2 class="l mr">聚集 ></h2>
<ul class="tab l">
<li><a href="">最新</a></li>
<li><a href="">大陆</a></li>
<li><a href="">日韩</a></li>
<li><a href="">热播</a></li>
</ul>
<div class="clear"></div>
</div>
<div class="tv-show">
<div class="big-show l mr">
<a href="">
<img src="http://ykimg.alicdn.com/develop/image/2019-02-13/ed026566424880372286e5d5bafbf28c.jpg"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</div>
<ul class="tv-tab l">
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li>
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
</ul>
<ul class="tv-tab l">
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li class="mr">
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
<li >
<a href="">
<img src="http://ykpic.alicdn.com/haitun-image/prod/compress/20190103/01ceb88d2d75f7e8fff266316808b974.jpg?x-oss-process=image/resize,w_290/interlace,1/quality,Q_100/sharpen,100"><br>
<span>看中国：宁夏</span>
</a><br>
<small>低调的宁夏 没了四级</small>
</li>
</ul>
</div>
</div>
</div>
</body>
</html>点击 "运行实例" 按钮查看在线实例
总结：
定位绝对定位是和相对定位一起使用的，一些有用的边框与背景样式可以很***。边框圆角与透明度背景
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