jQuery: Display Warning Icon Inside a TextBox

Here's a quick example on how to display a warning icon inside a TextBox when validation fails.

<head>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
     <style type="text/css">
        .warning{
            background: url(warning.png) no-repeat;
            padding-left: 18px;
            border:1px solid #ccc;
        }
    </style>
    <script>
     $(function () {
               $("#txt").keypress(function (e) {
               //if the letter is not digit then display error and don't type anything
               if (e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57)) {
               //attach css
                    $("#txt").addClass("warning");
                    $("#txt").val("");
                    return false;
                }
                else{
                     $("#txt").removeClass("warning")
                }
               });
           });
    </script>
</head>
<body>
    <input type = "text" id="txt"/>
</body>

You can see the actual demo here: http://jsfiddle.net/xoh7jm3c/10/