纯css下拉菜单 带一体化小三角装饰


<html>
	<head>
		<meta charset="utf-8">
		<title>下拉菜单title>
		<style>
			.select {
				margin: 50px 500px;
				width: 180px;
				text-align: center;
			}
			
			.select a {
				color: #fff;
				text-decoration: none;
			}
			
			.select ul,
			.select li {
				margin: 0;
				padding: 0;
				list-style: none;
			}
			
			.select span {
				line-height: 46px;
				background-color: #41b1d9;
				display: block;
				margin-bottom: 20px;
				position: relative;
				z-index: 2;
				border-radius: 5px;
				-webkit-transition: all .2s ease-in;
				transition: all .2s ease-in;
			}
			
			.select span a:after{
				content: " ";
				display: inline-block;
				width: 0;
				height: 0;
				font-size: 0;
				line-height: 0;
				border-bottom: solid 6px #fff;
				border-left: solid 4px transparent;
				border-right: solid 4px transparent;
				vertical-align: 1px;
				margin-left: 10px;
				-webkit-transition: all .2s ease-in;
				transition: all .2s ease-in;
			}
			
			/*给以整体的阴影和圆角 但是不能overflow*/
			.drop {
				left: 0;
				right: 0;
				top: -9999px;
				box-shadow: 0 0 2px 0 rgba(0, 0, 0, 0.2);
				border-radius: 5px;
				position: absolute;
				z-index: 1;
				-webkit-transform: translateY(-50px);
				transform: translateY(-50px);
				opacity: 0;
				-webkit-transition: all .2s ease-in;
				transition: all .2s ease-in;
			}
			
			/*给送个下拉助攻*/
			.select:hover span{
				background-color: #1f93bc;
			}
			
			.select:hover span a:after{
				-webkit-transform: rotate(180deg);
				transform: rotate(180deg);
			}
			
			.select:hover .drop{
				position: static;
				opacity: 1;
				-webkit-transform: translateY(0);
				transform: translateY(0);
			}
			
			/*一个很重要的三角形*/
			.drop li:first-child:before {
				content: " ";
				font-size: 0;
				line-height: 0;
				margin: 0 auto;
				display: block;
				box-shadow: 0 0 2px 0 rgba(0, 0, 0, 0.2); /*配合整体一样的投影*/
				background-color: #fff;
				width: 10px;
				height: 10px;
				-webkit-transform: rotate(45deg); 
				transform: rotate(45deg); /*一个正方形倾斜四十五度就是三角了  但是要把下半部分藏起来*/
				position: relative;
				top: -5px; /*果断的露出上半部分*/
				z-index: 1; /*果断的隐藏下半部分*/
				-webkit-transition: all .2s ease-in;
				transition: all .2s ease-in;
			}
			.drop li a {
				color: #888;
				line-height: 46px;
				border-bottom: solid 1px #eee;
				font-size: 14px;
				display: block;
				background-color: #fff; /*要有背景色才能盖住呀*/
				position: relative;
				z-index: 2; /*这里很重要 要挡住三角形的下半部分*/
				-webkit-transition: all .2s ease-in;
				transition: all .2s ease-in;
			}

			/*以下两块 控制第一个和最后一个LI要圆角  因为最外边的div没有overflow 也不可以overflow*/
			.drop li:first-child a{
				border-top-left-radius: 5px;
				border-top-right-radius: 5px;
				margin-top: -10px;
			}
			.drop li:last-child a{
				border-bottom-left-radius: 5px;
				border-bottom-right-radius: 5px;
				border-bottom: none;
			}
			
			/*hover事件给了li  先改变三角 再改变a*/
			.drop li:hover:before{
				background-color: #41b1d9;
			}
			.drop li:hover a {
				background-color: #41b1d9;
				color: #fff;
			}
		style>
	head>

	<body>
		<div class="select">
			<span><a href="javascript:void(0);">鼠标浮上来a>span>
			<div class="drop">
				<ul>
					<li>
						<a href="javascript:void(0);">下拉菜单一a>
					li>
					<li>
						<a href="javascript:void(0);">下拉菜单二a>
					li>
					<li>
						<a href="javascript:void(0);">下拉菜单三a>
					li>
					<li>
						<a href="javascript:void(0);">下拉菜单四a>
					li>
				ul>
			div>
		div>
	body>

html>

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