Edit in JSFiddle

Result
HTML
JavaScript

<body>
<p id="hiddenP">This is paragraph element.</p>
<button id="myButton">Click Me</button>
</body>

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