Vertical Tabs strip is negatively affected by #brave-web-view-rounded-corners

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Description

When flag is Enabled, which is being set to Enabled by the browser's variations feature, it affects Vertical Tabs strip in two different ways:

1. If the Sidebar is pinned to the opposite side to Vertical tabs, the vertical tabs strip will look weird on mouseover.
2. If the Sidebar is pinned the same side as the Vertical tabs, the vertical tab strip will be thicker than what it is supposed to be, it doesn't look weird as point one, just thicker, so the buttons looks misaligned and not centered anymore.

Recording.mp4

Steps to reproduce

1. Enable brave://flags/#brave-web-view-rounded-corners

2. Use Vertical tabs

3. go to brave://settings/appearance and Sidebar section

4. toggle between Show on the right and Show on the left and you will see the VT looking thicker.

5. Enable Expand vertical tabs panel on mouseover when collapsed

6. when mouseover, VT should display a weird cutoff border if the sidebar is Shown on the opposite side of the VT.

Actual result

Weird border being added

Expected result

no weird border or thickness in VT when flag is enabled.

Reproduces how often

Easily reproduced

Brave version (brave://version info)

1.76.2 Chromium: 132.0.6834.83 (Official Build) nightly (64-bit)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

[rebron]

This is missing a step because you resized the vertical tab strip, that's not the usual width. Double clicking on the resize window will bring it back to right width.

You're right that in step 4 there's a padding issue/bug from toggling that option.

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The other video and information from OP was when I was clueless what was the real reason, until I remembered variations, and how rounded corners get enabled by variations on the restart of a new user data.
I only updated the title but no other real information, but also left the video since it shows how sidebar on one side will affect this bug, and how it can be 'mitigated' by having sidebar on the same side as VT. (Not practical, unless sidebar is hidden)

This is how it is reproduced in a totally and completely User Data created from CMD and don't change anything at all anywhere:

1. Created User Data (brave.exe --user-data-dir=%USERPROFILE%\Desktop\TEMP)
2. Right click -> Toggle Vertical tabs
3. Collapse the VT and expand it to show there is no issue
4. chrome://restart to restart the browser (so the variations and therefore the rounded corners get enabled)
5. Expand VT -> ugly VT

Recording.mp4