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 ...

Include any extra CSS and JavaScript in the html file. If you have any images, load them from Unsplash or use solid colored rectangles. The user will provide you with notes in blue or red text ...

in that while it parses and renders HTML and CSS with JPEG and PNG image support, it does so only with a subset of HTML and is not tolerant of any malformations. There is also no JS support ...