This app is a classic hello-world type JS project for starter. But it is very much worth doing for a beginner who want to learn HTML, CSS and JS. The best part of it for me being a Python programmer is being able to figure out how CSS works. the JS part is relatively easy if you are comfortable to Python programming. I found that it is crucial as to how you should organize your element structure together with the CSS class naming convention. After googling for a while I learnt about the BEM naming convention, which is very much useful in keeping the DOM tree clean and easy to understand. BEM has also helped to avoid building up CSS selector in a nested structure, which is usually hard to understand and easy to catch bugs.

To run this app, clone the project and open index.html with a modern web browser. Below is a screen shot you would expect to see: