[PR Follow up 25547] - Still see white separator and dotted toolbar separator line is shown the vertical tab view only

[MadhaviSeelam]

Description

Originally, when I tested the PR brave/brave-core#25547 (comment) in 1.72.22, I've passed mostly. However, one issue I have seen is what looked like specs instead of a line in the toolbar in vertical tab view. I tried to reproduce the issue in 1.72.32 and I am seeing original white separator line, (instead of not so white-ish), dotted toolbar separator line in the dark theme. So, it appears #41055 issue may not have been fixed. Also, I am not seeing an expected subtle separator line in a new window

Steps to reproduce

1. Install 1.72.32
2. launch Brave
3. verified the flag brave://flags/#brave-web-view-rounded-corners is disable
4. switched Brave to Dark theme via brave://settings/appearance
5. switched to vertical tab view via tab context menu
6. A white separator line is shown
7. dotted toolbar separator line shown
8. installed https://chromewebstore.google.com/detail/just-black/aghfnjkcakhmadgdomlmlhhaocbkloab
9. White separator line is no longer shown but the dotted toolbar separator line is shown

Actual result

White separator line and dotted toolbar line is shown

2024-09-23_10h18_49.mp4

New window:

Original window	new window	expected results

Expected result

White separator line and dotted toolbar line should not be shown with Brave dark theme

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.72.32 Chromium: 129.0.6668.59 (Official Build) nightly (64-bit)
Revision	ccf542edfa3f211320afb393a11241d5366a173d
OS	Windows 11 Version 23H2 (Build 22631.4169)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

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

Miscellaneous information

@simonhong @rebron

cc: @qa