What does the "Unknown Word" error in SvelteKit with [vite] [postcss] mean?

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The "Unknown Word" error in SvelteKit with [vite] [postcss] usually means that the PostCSS parser encountered a word or syntax that it does not recognize or understand. This error can occur when using certain CSS syntax, such as CSS grid or custom properties, that are not yet supported by the PostCSS version used in SvelteKit. Upgrading the PostCSS version, updating the syntax used, or disabling PostCSS altogether may resolve this error.