使用css让表头固定的方法

<div>
	<div class="table-head">
		<table id="contentTable">
			<thead>
				<tr>
					<th><input type="checkbox"/></th>
					<th>xxxxx</th>
					<th>xxxxx</th>
					<th>证件号码</th>
					<th>姓名</th>
					<th>性别</th>
					<th>xxxxx</th>
					<th>出生日期</th>
					<th>xxx</th>
					<th>xxx</th>
					<th>ssss</th>
					<th>xxxx</th>
					<th>ccccc手机</th>
					<th>家庭住址</th>
					<th>xxxxx</th>
					<th>xxxxx</th>
					<th>xxxxx</th>
					<th>修改日期</th>
				</tr>
			</thead>
			<tbody>
				<tr>
                        //21个td  省略
                    </tr>				
			</tbody>
		</table>
	</div>
</div>

/** 这是css */
body{overflow-y: hidden}
#contentTable tbody { display: block; height: 520px; overflow-y: scroll; }
#contentTable thead,
#contentTable tbody tr { display: table; width: 100%; table-layout: fixed; /**表格列的宽度由表格宽度决定，不由内容决定*/ text-align: center; }
 
/**每一个th都要和对应的td宽度相同，如果不设置，则默认均分宽度，我设置的都是一些内容较多的，比如说身份证号码，电话，住址等*/
#contentTable tr th:nth-of-type(1),#contentTable tr td:nth-of-type(1){width: 1.5%;}
#contentTable tr th:nth-of-type(2),#contentTable tr td:nth-of-type(2){width: 8.5%;}
#contentTable tr th:nth-of-type(3),#contentTable tr td:nth-of-type(3){width: 7%;}
#contentTable tr th:nth-of-type(4),#contentTable tr td:nth-of-type(4){width: 8.5%;}
#contentTable tr th:nth-of-type(8),#contentTable tr td:nth-of-type(8){width: 5%;}
#contentTable tr th:nth-of-type(9),#contentTable tr td:nth-of-type(9){width: 5%;}
#contentTable tr th:nth-of-type(12),#contentTable tr td:nth-of-type(12){width: 8.5%;}
#contentTable tr th:nth-of-type(13),#contentTable tr td:nth-of-type(13){width: 6%;}
#contentTable tr th:nth-of-type(14),#contentTable tr td:nth-of-type(14){width: 15%;}
#contentTable tr th:nth-of-type(16),#contentTable tr td:nth-of-type(16){width: 5%;}
#contentTable tr th:nth-of-type(18),#contentTable tr td:nth-of-type(18){width: 5%;}
 
/**这一个重要：写完上面的看效果应该是表头和内容对不齐。我们需要的是调节0.4em中的0.4，试着变大变小就能看到区别，我试了，刚好跳到0.4，所有的列都能垂直对齐*/
#contentTable thead { width: calc( 100% - 0.4em);/*表头与表格垂直对齐*/ }

#sTable::-webkit-scrollbar{
    width:0px;
    opacity:0;
    -webkit-overflow-scrolling: touch;
}