Rating component using JS CSS HTML, added|Alert when no rating chosen

Hello everyone, It's been a while since I posted anything here. Well, I have been learning Javascript, also I was pretty focused on backend development in school projects. So, I put at your disposal my solution for the frontend mentor interactive rating component challenge. I have tried to do my best to make close to the design as well as added some stuff that I found useful:

• Users aren't allowed to move the submitted page after clicking the submit button unless they have chosen a rating, if they didn't an alert will appear to tell them that they should choose one.
• I added a back button in the submitted page.

I hope you would check the code and the live site and provide me with your feed back as for the questions that I have they are the following:

• What are the best practices when it comes to popup windows?
• When do you think someone is ready for working as a frontend developer, I mean what is the minimum knowledge?