How do I correctly set routes in a Shopify Remix App?

I want my product page to have this link: /app/products/$handle. Currently, it is under /products/$handle, and the Polaris design doesn’t work on this page. I am using Polaris design, but it looks like it isn’t being applied.

I have tried placing my products.$handle.jsx file into the routes/products folder. I also tried renaming it to $handle.jsx and putting it into the routes/products folder, but nothing works, and the design of this page remains unchanged.

I want my product page to have this link: /app/products/$handle. Currently, it is under /products/$handle, and the Polaris design doesn’t work on this page. I am using Polaris design, but it looks like it isn’t being applied.