Wow, thank you so much for the info and such a kind and honest reply. You talk just like me. ^^ Haha, I never want you to shut up.
I have attached two pictures to be clear on what I mean. The first one is SquareCorners theme atlas. The second one is windows 7 theme atlas.
The windows 7 theme atlas has thick borders in every window but changing the BorderWidth and PaddedBorderWidth to 0 in WindowMetrics gives me thin borders everywhere except this metro calendar, wifi, battery...etc. tray icon popups.
I hope the authors of theme atlases can shed some light on how they achieved thin borders.
@MrGRiM
@infinality
@hfb
@least1234
@bigmuscle
@ORelio
@NoelC
@laballu
@oomek
@GIL
@JoshuaVL1988
Thank you all!