Edit in JSFiddle

Result
JavaScript
HTML
CSS

$(document).ready(function () {
                $("#myDiv").hover(function () {
                    $(this).css("background-color", "red");
                }, function () {
                    $(this).css("background-color", "Green");
                });
            });

<html>
        <head>
        <title>CSS</title>
        </head>
        <body>
        <div id="myDiv">
        </div>
        </body>
        </html>

#myDiv
        {
        background-color:Green;
        width:200px;
        height:200px;
        }