Hugo deployment failed in cloudflare

Error: Error building site: POSTCSS: failed to transform “scss/main.css” (text/css). Check your PostCSS installation; install with “npm install postcss-cli”. See this feature is not available in your current Hugo version, see Frequently Asked Questions | Hugo for more information

hey guys, can anyone help me?
I built hugo locally and saved it on github.
Hugo’s theme uses postcss. This component needs to be installed using cli commands. What should I do?
I don’t know how to put the command’npm install postcss-cli’ into the environment variable?

Hugo itself needs to be either compiled with postcss/pipes support or you install one of the extended precompiled versions.

After that, you need to install postcss and postcss-cli AND all used plugins either locally in your site or globally in your system (npm install vs. npm install -g). Don’t mix the installation type, if postcss is installed globally then all other parts need to be there too.