It's called Dash, and it lets users learn how to use HTML, Javascript, and CSS by working through four projects of increasing difficulty. As you progress through the projects — starting by ...

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 ... to create scrap projects or files.

It allows you to edit PHP, HTML, CSS and JavaScript files, and it highlights the syntax ... recognition and building of the complete structure of PHP projects—all of these functions ensure easy work ...

HTMX as a mature project may not wind up working precisely ... they always seem to obfuscate the powerful trio of HTML, JavaScript, and CSS, which continues to win out in the end.