1.css文件：
div{
border: 1px solid red;
}
span{
border: 4px solid green;
}
html文件:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<!--link标签专门用来引入css样式代码-->
<link rel="stylesheet" type="text/css" href="1.css"/>
</head>
<body>
<div>div标签1</div>
<div>div标签2</div>
<div>div标签2</div>
<div>div标签2</div>
<div>div标签2</div>
<div>div标签2</div>
<span>span标签1</span>
<span>span标签2</span>
<span>span标签2</span>
<span>span标签2</span>
<span>span标签2</span>
</body>
</html>