Fix ESM types

[elchininet]

Following the recommendations in the TypeScript Handbook. This is to avoid TypeScript complaining about missing types when the ESM module is used:

Could not find a declaration file for module 'postcss-rtlcss'. '/path-to-project/node_modules/postcss-rtlcss/esm/index.js' implicitly has an 'any' type.
There are types at '/path-to-project/node_modules/postcss-rtlcss/index.d.ts', but this result could not be resolved when respecting package.json "exports". The 'postcss-rtlcss' library may need to update its package.json or typings.ts(7016)