<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$(":file").css("background-color", "red");
});
</script>
</head>
<body>
<form action="">
Name: <input type="text" name="user"><br>
File: <input type="file" name="myfile">
</form>
</body>
</html>