Flexbox / CSS / Javascript

Hello all , I'm pretty happy of what I've done for my first javascript challenge I resume learning javascript again !

I really need a feedback on this one I struggle with the input radio to keep them focus when the user is selecting a number and I haven't found how to do it like the design so I've done it with the dom and pop-up an alert telling which number have been selected that allow to see the number selected with the right background color then redirect the user to thanks page.

I think I could use less if...else statement and just use switch but at the moment I have no idea on how to do it. ( It always the case )

I'm open to any advice.

Thanks for reading