@media.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        @media all and (max-width: 500px){
            .box{
                width: 100px;
                height: 100px;
                background-color: red;
            }
        }
        @media all and (min-width: 500px){
            .box{
                width: 100px;
                height: 100px;
                background-color: yellow;
            }
        }
    </style>
</head>
<body>
<div class="box"></div>
</body>
</html>