2. HTML. We write HTML in files that end with the .html extension (like homepage.html).. To write HTML and CSS code, you’ll want to install a code editor.Nowadays, one of the most popular free ...

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.

AFAIK, CSS cannot affect the DOM tree. So, display: none just says the element should not be displayed, not that it should cease to exist. Style/structure separation and all that.

jsFiddle is the perfect solution; it provides a custom environment (based on user selections) to test (or fiddle with) your JavaScript, HTML, and CSS code right inside your browser.