resolveCSSVariables: Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'indexOf')

[zeevenn]

doocs/md#1126

Repro: test.ts

It should set resolveCSSVariables to false，then run success.

I think we can remove this feature and let user use postcss-custom-properties to handle css variables.

doocs/md#1131

[zeevenn]

like this: https://github.com/doocs/md/blob/main/packages/core/src/theme/cssProcessor.ts