Matthew S. Smith, Digital Trends:

Differences do appear when you dig deeper. Here’s the big one; Windows 10’s dark mode only applies to Universal Windows Platform apps. It doesn’t change older, legacy interfaces. That includes Explorer, Task Manager, and all the old Control Panel menus, some of which still don’t have their function replicated in Windows 10’s Settings Menu.

And:

We must again nitpick Microsoft’s approach, though, for a reason that’s as simple as it is silly. Edge opens an MSN home page by default. It’s a web page, not part of the application interface, so it doesn’t get the dark mode treatment. This also applies to the “blank” page that you can choose to select instead of MSN. You’ll always be greeted with a grayish-white page in Edge, unless you manually change the home page to a website with a dark background.

Safari has no such problem. Its default new tab page, which has a list of featured websites, will change its background to slate gray when dark mode is turned on.

Attention to the tiny details. When done right, it does show.