I'm trying to workout how to set the background of an iOS 10 today extension/widget to what looks like a default dark mode. In the image below you can see the Weather Underground today widget and it is dark. There are a few apps with a dark background and they all look like the same background/style so I'm thinking it maybe a specific dark mode that can be set in code rather than just fiddling with the view controller color/transparency - no matter how much I try to set the color and transparency manually in the story board I can't even get close to this effect.
You can't do this. The apps that look like this, are not updated for iOS 10 yet. You can see that it hasn't been updated, because it is expanded without showing the "Show less"/"Show more" button.