Demonstrate reactive-css-properties

To show off what reactive-css-properties can do, we need talented developers who want to show off their front end skills and grab the attention of the community. Your contribution is 100% crucial for the buy-in of prospective developers, I will do anything I can to support you.

## App ideas, just for inspiration.
- todo list
- stop watch
- three.js app styled from css in realtime
- compas
- calculator
- Awesome canvas visualisation
- Product configurator

## Any rules
Just three:
- Use the vanilla JS flavour of reactive-css-properties because this is the most understandable for all
- Use any libraries you want to make things quicker
- No copyrighted or IP protected material that will get us taken down