You cannot set environment variables inside a Walrus Site itself. Walrus Sites are fully static and publicly accessible: all site content and metadata are stored on-chain (Sui) and on Walrus, and there is no backend or server-side execution where environment variables could be injected or used.

For portal configuration involving environment variables, these are set in the .env.local file at the root of each portal directory you're working with, not on the static site itself.