He uses small background images that are places with CSS. Then, the classNames for the form elements are swithced with JavaScript. Marko also uses JavaScript to preloaded the custom images.

CSS Pseudo-elements in 100 Seconds Dive into the world of CSS pseudo-elements! Learn how to use ::before and ::after to add stylistic content without altering your HTML. Perfect for adding icons ...

Developed as a browser add-on, CSS Scan 2.0 allows developers to easily see and copy CSS details of any element on a website. Developed by the independent developer Guilherme, the add-on is quite easy ...

Google posted on Twitter "we recommend not adding meaningful content or symbols using ::before or ::after CSS pseudo-elements." Google said such content "might not be used for indexing your pages.