index.css

index.js

index.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>jQuery: Change the Look of a Paragraph</title>
  </head>
  <body>
    <p id="main">This is the main text</p>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
    <script>
      $("p#main").css('backgroundColor', '#000').css('color', '#fff');
    </script>
  </body>
</html>