codepen-hide-box
For beginers, a good challenge to train is to go on codepen.io and hide one of the box and then recreate the missing part.
I want to create a small chrome extension that allows you to hide the CSS box or the HTML box on http://codepen.io
Once the box is hidden, we can decide to show it again or show it again but with the content removed so you can start recreating the content of the box without seing any line of code of the solution.
This tool would allow me to create a new YouTube show where I randomnly recreate missing parts while commenting it out loud. Furthermore, it can look like a real world mission because sometimes you are called to debug a project where you have only access to css, or html but not both. This extension would make funny challenges that you'll be able to reproduce on your side.