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It appears that it would take significant work for IBM to make Carbon truly theme friendly. I find their layout system lacking and the documentation, though beautiful, complex and difficult to navigate. Carbon seems to me to be more component library than CSS framework. In my opinion, our current solution with Bootstrap seems like a simpler and potentially better solution for helping our teams move faster.
Notes
Documentation for React Components is not ideal.
It uses React Storybook with Readme, which is fine, but some of the stories cannot be viewed or copied because of the way story sets are written. See the story for DataTable: http://react.carbondesignsystem.com/?selectedKind=DataTable&selectedStory=with%20toolbar&full=0&addons=1&stories=1&panelRight=0&addonPanel=%40storybook%2Faddon-a11y%2Fpanel
Doing more than color theming is somewhat difficult (and likely brittle)
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