The openPage function in the app.js file has repeated code in each of the if/else blocks where it sets the display property of the different containers and adds the active class to the corresponding link item. I will suggest you improve this, by extracting the repeated code into a separate function that takes the container element and link item as arguments and sets their display and class properties accordingly. This would reduce duplication and make the code more maintainable.

Additionally, I will suggest you add comments to your code since it plays an important role in enhancing readability, facilitating maintenance, and clarifying intent. Clear, concise, and informative comments, can help make your code more accessible and understandable to other developers, even years down the line.