<html>
<head>
<style>
input:focus {
background-color: yellow;
}
</style>
</head>
<body>
<form action="/action_page.php" method="get">
First name: <input type="text" name="fname"><br><br>
Last name: <input type="text" name="lname"><br><br>
<input type="submit" value="Submit">
</form>
</body>
</html>