Shields onboarding pulsating ring should match (blurple) to the design

[MadhaviSeelam]

Description

Found while testing #27490. Shields onboarding pulsating ring,as per the design, should be blurple, however, it doesn't match in 1.63.x whether it's light or dark theme in Win 11.

Steps to Reproduce

1. Install 1.63.41
2. launch Brave
3. visit bbc.com

Actual result:

Shields onboarding pulsating ring may not match to the design

Dark	Light

Expected result:

Shields onboarding pulsating ring may should match to the design

Reproduces how often:

Easily

Brave version (brave://version info)

Brave | 1.63.41 Chromium: 120.0.6099.115 (Official Build) nightly (64-bit)
-- | --
Revision | c56c5ba04606284792201770bb6cb52d1ef367b6
OS | Windows 11 Version 22H2 (Build 22621.2861)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the nightly channel?

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 @aguscruiz
cc: @simonhong

[aguscruiz]

Here's the design:
https://www.figma.com/file/MFHpcXJMg2RUQpUJMAZZ4R/Desktop-Onboarding?type=design&node-id=4205%3A104829&mode=design&t=qTSKxAK2gz1Eg7Z1-1

In any case, it's no big deal. We can just leave it as it is if we have more important things to fix