4. https://www.sitepoint.com/javascript-important-ui-development/
5. https://www.smashingmagazine.com/2018/03/dynamic-functional-css-variables-javascript/
6. https://www.digitalocean.com/community/tutorials/understanding-the-dom-tree-and-nodes-in-javascript
7. https://www.freecodecamp.org/news/ajax-get-and-post-requests-explained-with-examples/