<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title></title>
<link rel="stylesheet" href="style2.css">
</head>
<body>
<div class="red"></div>
<div id="greendiv"></div>
<div class="red"></div>
</body>
</html>
div{
width:100px;
height:100px;
display:inline-block;
margin:15px;
}
.red{
background-color:red;
}
#greendiv{
background-color:green;
}