This is a html code editor or html IDE. i have made this using html,sass (css),bootstrap and javascript and some javascript Library. ( Jquery,popper)
Bootstrap - Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development.Bootstrap utilizes Sass for a modular and customizable architecture.
Jquery - jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers.
Popper - Popper. js is a positioning engine, its purpose is to calculate the position of an element to make it possible to position it near a given reference element. Popper. js has zero dependencies.
Hope all the above information will be useful for your learning.