I tried tweaking my settings through the Windows 10 settings application, and I found out this weird combo: when I turn on "dark mode" in the settings below, windows will directly assign the background tabs red; however, if I disabled the option, the background tab becomes white, which is not the defualt Windows 10 dark mode behavior. In the standard dark mode, the background tabs will become a darker shade of grey and the control buttons next to the last tab is white.
Is it something to do with the secondary color settings in this application?


Enabling dark mode yields the red background mentioned above and automatically adjusts the Windows settings on the second image above. If I disable the "title bars and Windows borders," a weird white background tab appears -- shown in the image below.

Also, just asking -- could it be Curtains that is adding an additional border around my application window? You were using a separate title bar theme than mine. My title bar theme is the windows 10 default theme. This part is regarding the slice-of-space matter.
@RND -- thanks for your reply, but I'm already using TaskbarX but am looking for a possibility to unify all the settings in Curtains. I'll try digging into the native Windows method