@geki007 -- Tested the issue on Chrome Dev# 54.0.2832.2 on Windows and did not find any style issue in incognito windows.
Could you please let us know what exactly the style issue you are observing.
Thanks in Advance.

see the red circle in the screenshot ... for me it looks like the cant of the active tab has a nice bold line when it overlaps the inactive tab but not when it doesn't overlap

if you say it's ok it could also be ok

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@geki007 -- Tested the issue again on Chrome Dev# 54.0.2840.8 on Windows and could not observe anything as mentioned in the screenshot.
Could you please let us know whether there was any specific theme installed.
Thanks in Advance.

sry i'm not good in painting but i try it again
for me it looks like the blue line i painted should be there
if you still don't see it ... i think i'm the problem and you can close the bug :)
no theme, just incognito window

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Are you talking about the tab border that was intentionally added in an effort to visually separate tab strip and the window frame more on darkish themes, implemented in  issue 585470 ?

i'm not sure if it's the same ... but yes talking about the border
i just think there is no border or a ~1px bad positioned border where i painted the blue line

the border looks different where it overlaps another tab

Attaching the screenshot by checking on Chrome Dev# 55.0.2853.0 and Chrome Canary# 55.0.2858.0.
Could some one from incognito team please look into the issue and update.
Thanks in Advance.

Note: Removing Needs Bisect label as of now.

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do you need feedback from me?

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@geki007 -- Could you please respond to Comment# 10 by verifying on latest stable# 55.0.2883.75 and update the issue which would help us triaging further.
Thanks in Advance.

not sure what i should respond to Comment #10
in Comment #10 i can see it and it's still in latest stable and dev

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Just to clarify, I *think* I see what this is about. I attached a HiDPI screenshot — there's no bug, but the semi-transparent border does make it look like there's a border where the tab overlaps the other tab, and no border where it doesn't. The tab looks thicker where it overlaps the other tab. It's purely a perceptual thing.

To the reporter: does that sound right?

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To put it another way, I think this looks more natural from a distance even though it's "wrong" up close (I just shifted the bottom half of the tab over by 1px in an image editor).

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yes, this sounds very right!

if it's a "feature" i can live with it, but for me screenshot in comment #21 looks better (but not perfect ... think because of just shifted)

Cc'ing sdy@ for update as per C#22.

ajha@: I don't have anything to add right now :). I just dropped in to help clarify the issue, I don't work on design (or Windows).

Adding proper bug label for someone from the respective team for more inputs on this.

This is as intended, although I agree that it's a bit odd as a design (but it's what our visual designer wanted).

The main issue here is that a single semitransparent stroke appears like a "border" or a "shadow" depending on what the relative colors of the foreground and background are.  The main way we are dealing with this is by implementing the engineering needed to avoid an #FFFFFF frame color in incognito windows by default on Win 10, since in that case, you're kind of screwed no matter what.

The proposal in comment 21 effectively separates things into a "border region" (only drawn where tabs overlap) and a "shadow region" (only drawn where they don't) that's physically outside it.  This looks OK in high DPI, but I suspect not as good in 1x, where it would make the tab borders feel thicker (if the border was drawn everywhere) or the two feel disconnected (if not).