Blank/grey tab is shown in between tabs after scrolling down to the last tab and scrolled back up in light theme

[MadhaviSeelam]

Description

@kjozwiak noticed this issue initially. Reproduced in 1.51.87 while testing #29692. If Brave browser is set to light theme and after enabling vertical tab view, scrolling down to the last tab and scrolling back up, a blank/grey tab is shown in between tabs.

Steps to Reproduce

1. Install 1.51.87
2. launch Brave
3. open brave://flags
4. select Enabled for #brave-vertical-tabs
5. click Relaunch
6. visited bbc.com
7. right click on the tab to open context menu
8. enable Use vertical tabs
9. add few tabs in the vertical sidepanel to enable scroll
10. scroll down to the last tab which will be highlighted to grey
11. scroll back up

Actual result:

blank grey tab is shown in between tabs when scrolled back up.

2023-04-17_11h19_43.mp4

Expected result:

Tabs should be highlighted with grey similar to 1.52.x?

Reproduces how often:

Brave version (brave://version info)

Brave | 1.51.87 Chromium: 112.0.5615.49 (Official Build) beta (64-bit)
-- | --
Revision | bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS | Windows 11 Version 22H2 (Build 22621.1555)

Version/Channel Information:

• Can you reproduce this issue with the current release? N/A
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the nightly channel? No

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

@rebron @sangwoo108

cc: @brave/qa-team

[kjozwiak]

The above requires 1.51.100 or higher for 1.51.x verification 👍

[stephendonner]

Verified PASSED using

Brave	1.51.109 Chromium: 113.0.5672.63 (Official Build) (x86_64)
Revision	0e1a4471d5ae5bf128b1bd8f4d627c8cbd55f70c-refs/branch-heads/5672@{#912}
OS	macOS Version 11.7.6 (Build 20G1231)

Reproduced the issue using 1.51.87; confirmed the gray tab at the bottom, after scrolling down and back up

Steps:

1. installed 1.51.109
2. launched Brave
3. ensured I was using the Light theme
4. switched to using vertical tabs
5. opened a bunch of tabs
6. looked at the bottom tab(s)

Confirmed the tab highlight was the right color/style, and there were no blank/gray tabs after scrolling up and down