CSS响应式布局问题

麻烦大佬帮忙看看为什么不能根据页面调整大小。

明明已经设置了响应式布局,调整浏览器页面没有反应。

<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			* {
				margin: 0; padding: 0;
				border: none; list-style: none;
			}
			@media screen and (max-width:640px) {
				.item {
					width: 50%;
				}
			}
			@media screen and (max-width:768px) {
				.manu-s {
					display: block;
				}
				.menu-b {
					display: none;
				}
				.item {
					width: 33.33%;
				}
			}
			@media screen and (max-width:1024px) {
				.item {
					width: 25%;
				}
			}
			header {
				position: fixed;
				background-color: #696969;
				height: 50px;
				width: 100%;
			}
			.logo img{
				display: block;
				height: 50px;
				float: left;
				margin: auto 20px;
			}
			.menu-b {
				float: right;
			}
			.menu-b li {
				color: white;
				height: 50px;
				line-height: 50px;
				float: left;
				padding:0 20px;
			}
			.menu-s {
				display: none;
				float: right; margin-right:20px;
				color: white; font-size: 18px; line-height: 50px;
			}
			.menu-s .menu {
				cursor: pointer;
				width: 100%;
				position: fixed;
				top: 50px;
				left: 0;
			}
			.menu-s .menu li{
				display: none;
				text-align: center;
				width: 100%;
				background-color: #808080;
				opacity: 0.5;
				border-top: white 2px solid;
			}
			.menu-s .menu:hover li{
				display: block;
			}
			.advertise img{
				display: block;
				width: 100%;padding-top: 50px;
			}
			.item {
				float: left;
				padding: 20px 10px 20px;
				width: 20%;
				box-sizing: border-box;
			}
			.item img {
				width: 100%;
				display: block;
				box-shadow: 0 0 5px 2px #888888;
				border-radius: 3px;
			}
			
		</style>
	</head>
	<body>
		<header>
			<div class="logo">
				<img src="images/logo.png" >
			</div>
			<ul class="menu-b">
				<li>文章</li>
				<li>素材</li>
				<li>活动</li>
			</ul>
			<nav class="menu-s">menu
				<ul class="menu">
					<li>文章</li>
					<li>素材</li>
					<li>活动</li>
				</ul>
			</nav>
		</header>
		<div class="advertise">
			<img src="images/top-bg.png" >
		</div>
		<div class="banner">
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
			<div class="item">
				<img src="images/1.jpg" >
				<p>迷你摄影展</p>
				<p>11111111111</p>
			</div>
		</div>
	</body>
</html>

 

把以下css 查询 判断 删除即可

@media screen and (max-width:640px) {


				.item {


					width: 50%;


				}


			}


			@media screen and (max-width:768px) {


				.manu-s {


					display: block;


				}


				.menu-b {


					display: none;


				}


				.item {


					width: 33.33%;


				}


			}


			@media screen and (max-width:1024px) {


				.item {


					width: 25%;


				}


			}

 

 

动态图演示

应该设置范围,并且放到样式的最后面