Try this:
<!DOCTYPE html>
<html>
<head>
<title>Changing font-size using Media query</title>
<style>
@media (min-width: 550px) {
body {
font-size:25px;
}
}
</style>
</head>
<body>
<h1>Studytonight</h1>
</body>
</html>
You were adding the background color extra. Please don't add any additional property
