Edit in JSFiddle

Result
JavaScript
HTML
CSS

$(document).ready(function () {
        $("#myDiv").hover(function () {
            $(this).addClass("thisDiv");
        });
        $("#reset").click(function () {
            location.reload();
        });
    });

<html>
        <head>
        <title>addClass</title>
        </head>
    <body>
        <span id="myDiv">
        Hover Me
        </span>
        <br />
        <input type="reset" id="reset" value="Reset" />    
        </body>
        </html>

.thisDiv
        {
        background-color:Red;
        margin-left:400px;
        width:200px;
        height:200px;
        display:block;
        }