这个代码为什么网页端什么也不显示？
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>div css </title>
<style type="text/css">
.div1{
background:olive;
text-align:center;
font-family:仿宋;
font-size:40px;
width:500px;
height:400px;
line-height:400px;
margin-left:300px;
margin-top:300px;
}
#idselector{
color:navy;
font-size:40px;
}
</style>
</head>
<body>
<div class="div1">
今天天气很不错
</div>
<span id="idselector">体检通过</span>
</body>
</html>
```
