brave://welcome modal has an 8px border around it

Description

White 8px border is added to brave://welcome

Noticed on 1.22.22 by @LaurenWags ; was not present on 1.22.19.

Suspected PR that broke this: https://github.com/brave/brave-core/pull/7919

Steps to Reproduce

1. Install 1.22.22
2. Visit brave://welcome

Actual result:

Expected result:

No white 8 pixel border

Reproduces how often:

100%

Brave version (brave://version info)

1.22.22

Version/Channel Information:

Nightly

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

[LaurenWags]

@GeetaSarvadnya try a newer Nightly like 1.22.24

[stephendonner]

Verified FIXED on nightly using

Brave	1.22.34 Chromium: 89.0.4389.48 (Official Build) nightly (x86_64)
Revision	0fe3c4589a6cf5ce719d167834dfa9cd8978937a-refs/branch-heads/4389@{#873}
OS	macOS Version 11.2.1 (Build 20D74)

I checked dark and light versions of brave://welcome, as well as brave://rewards and brave://wallet panels.

Screenshots: