Responsive Summary Component using vanilla css and javascript

Made this with completely vanilla CSS and JavaScript.

• What did I find difficult while building the project?
• The difficulties faced in this project were usage of css variables and picking up data from .json file using javascript and populating the list of element along with their colors. so any better approach suggestion would be hugely appreciated.
• What are the best practices to use javascript here in this project ?
• I have used vanilla js but only used functions for implementation, if in future I want to implement such projects what are the best practices to manage the structure of vanilla javascript.