How to get senstive information in vite react

[sunilgithubuser]

Hi,
I tried sensitive information to fetch as mentioned like example here but i am getting undefined
const SECRET_KEY = process.env.SECRET_KEY;
https://import-meta-env.org/guide/extra-topic/sensitive-environment-variables.html

what i want is i don't want to expose this in public so i didn't add here in .env.example that variable SECRET_KEY
i am expecting Test123

i am setting
"preview": "cross-env SECRET_KEY =Test123 import-meta-env -x .env.example.public && vite preview"

is there any example to read sensitive information in vite react without exposing in front end .Thanks.