In bootstrap by using .modal & .fade classes you can implement popup modal with animation effect. You can apply CSS to your Pen from any stylesheet on the web. Have you ever clicked on an image on a webpage that opens up a larger version of the image with navigation to view other photos? You can use the transitions from animate.css or create your own transitions.. DOWNLOAD VERSION 1.0 If you want to change the default animation, you can do so by creating your own css animation. Responsive modal or popup are common features in a web application. At the end of the scale-up animation, the modal window visibility is changed (using the .modal-is-visible class) to reveal its content.