Separator is not clearly shown for adjacent inactive tabs in split view

[MadhaviSeelam]

Description

Found while testing #39486. If Split view is enabled via brave://flags/#brave-split-view and go to split screen view, some of the adjacent inactive tabs do not show separator. This happens both in light and dark theme.

Steps to reproduce

1. Install 1.74.4
2. launch Brave
3. enable split view via brave://flags/#brave-split-view
4. select split view via context menu of a tab
5. notice inactive adjacent tabs do not show separator

Actual result

light	dark

Expected result

Separator should show

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave | 1.74.4 Chromium: 131.0.6778.39 (Official Build) beta (64-bit)
-- | --
Revision | 15328654b03f358466ab746b5d12a68e7fdb5017
OS | Windows 11 Version 23H2 (Build 22631.4460)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

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

Miscellaneous information

@rebron @aguscruiz @simonhong
cc: @brave/qa-team

[aguscruiz]

Updated design here:
https://www.figma.com/design/Dt0iJdVaaAj7DikWLO1P7I/Split-view-%2F-Sidebar-browsing?node-id=2469-11836&t=bZFVWJMSvlzoefYl-1

[simonhong]

Working on this.

[simonhong]

@aguscruiz In the figma, DesktopBrowser/TabBar/Split View - Divider token is used but I couldn't find it from generated file nala_color_id.h like below.
Do we need to bump nala to use it?

[aguscruiz]

@simonhong maybe! I guess Nala is a bit more behind than what I thought.

[aguscruiz]

Let me know if you'd prefer for me to give you the primitive values instead to unblock you. I have them too

[simonhong]

Let me know if you'd prefer for me to give you the primitive values instead to unblock you. I have them too

Code is ready but it seems it's resolved when brave/brave-core#26995 is merged?

[aguscruiz]

Probably yes! Let's see.