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. A quick tour ...

HTML and CSS form the basic coding languages for web ... Business apps built with web technologies, particularly HTML, CSS, and JavaScript, are in great demand since they can run natively on ...

The new release brings improvements to JavaScript heap profiles, CSS code formatting ... the semantic highlighting of JavaScript source in HTML files with what is seen in normal .jscode files.