Salpit

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

</head>
<body>

    <p>Hi I'm learning jQuery</p>
    <p>Second paragraph</p>
    <button id="btnChange">Change Content</button>

    <script>
        $(document).ready(function () { // wait for webpage finished loading (ready)
            $("#btnChange").click(function () {
                $("p").html("New content here");

                $("p:first").css("color", "red");
            });
        });
    </script>
</body>
</html>