This is an easy to use HTML and CSS playground that can easily be embedded. See an example here.

It has the following features:

• Realtime updating preview
• Save as HTML functionality
• Quick share button
• Reset to original button
• Very lightweight
• Standalone design

This project is designed to work with a specific online learning system but should work anywhere that allows embeds/iframes.

Your code isn't hosted or logged anywhere, it's encoded in a URL parameter then decoded via JavaScript. This means the project doesn't need a database or anything else. It does mean the amount of code is limited to the maximum URL size that your browser supports - but this is very unlikely to be a problem. Note that that this project is not designed for security, don't open or embed URLs that you don't trust.

Load up the editor here or on your own host. Then you can write your HTML and CSS. You can switch between languages by clicking the language name, which will show a dropdown. If you want to share your code you can hit the blue link icon in the top right that will copy the URL to your clipboard - which you can then share or place in an iframe element.