Transpilation generates unnecessary fallback inside @support. For example, when lab() is used inside @supports (color: lab(0% 0 0)), lightningcss generates @supports (color: lab(0% 0 0)) inside it.

playground

These kinds of input happens in Vite because Vite runs lightningcss two times. First to transpile CSS to make other plugins able to process CSS, second to minify the final CSS.
Original issue: vitejs/vite#16354