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.

You can do impressive things with HTML and CSS. There are several examples on JSFiddle where developers implement the Sieve of Eratosthenes, a way to calculate prime numbers, with HTML and CSS. That ...

How to build a website with programming languages HTML, CSS and JavaScript. ... For example, you might like yellow and red, but using both of them at once might be a bit jarring for visitors.