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In the following example, the : has been missed after ‘background’.
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Guidelines for creating a dark theme
Unfortunately, there is no guaranteed way to find out if text is inside, outside or partially inside the data blocks. We recommend the following steps to ensure that text labels work well when using dark themes:
use dark application background
use dark colours for chart data
use light (e.g. white) text for chart data, which can be defined as per the screenshot below