When selecting a theme in Personalization, the toolbar doesn't change completely, unless I'm using the Groupedbar Compact toolbar (I prefer to use Standard!).
I've got a screenshot, which you can view here: https://cdn.discordapp.com/attachments/377175958039560218/766409606867189780/unknown.png.
The toolbar DOES go completely dark if I have two windows side-by-side.
Steps to Reproduce:
1. Use a monitor with 4k capability
2. Set toolbar to Dark Mode.
A chunk of white was cut into the toolbar, while the rest was dark.
The toolbar should have gone completely to dark mode.
User Profile Reset: No
Version: 184.108.40.206 (x64)
Build ID: 8349ace3c3162073abd90d81fd06dcfb6b36b994
CPU threads: 12; OS: Windows 10.0 Build 18363; UI render: Skia/Vulkan; VCL: win
Locale: en-US (en_US); UI: en-US
The 'Preinstalled' themes include raster background gradients as PNG that will not scale to fit 4K layouts. They are not a substitute for work needed to support os/DE theme colors for Windows 10 UWP 'Dark Mode', see also bug 118320
Not clear it is worth correcting the 'Preinstalled theme' PNGs for HiDPI use otherwise.
Would make this a duplicate of bug 131023 (same issue with less than 4k). And solve everything with implementation of own themes (see bug 125217).
*** This bug has been marked as a duplicate of bug 131023 ***