Currently there are two UI themes, “Salesforce” and “Salesforce Classic.” How could you figure out which theme is enabled?

By calling describeTheme() , looking at userUiSkin property of returned object.

There is no way to figure out UI theme from API, because Customer Portal users can't access this object.

By calling getUserInfo(), looking at userUiSkin property of returned object.

There is no way to figure out UI theme from API, because Partner portal users can’t access this object.

Answer:
By calling getUserInfo(), looking at userUiSkin property of returned object.

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