Edit in JSFiddle

<body>
    <div class="myDiv1 myDiv2">This is div.</div>
    <button id="myButton">Click Me</button>
    <button onclick="location.reload()">Reset</button>
    </body>

$(document).ready(function()
    {
    $("#myButton").click(function()
    {
    $(".myDiv1.myDiv2").css({'font-size':'20px','background-color':'Orange'});
    });
    });