[Desktop] Small rectangle overlaps top scrollbar arrow in settings

[btlechowski]

The rectangle is not clickable thus makes using the top scrollbar arrow harder.

Steps to Reproduce

1. Open brave://settings
2. Observe the top scrollbar arrow

Note: The rectangle is best visible in dark theme

Actual result:

small rectangle overlaps top scrollbar arrow in settings.
The rectangle blocks click events.

Expected result:

small rectangle does not overlap top scrollbar arrow in settings.
Top scrollbar arrow is fully clickable

Reproduces how often:

100% repro rate

Brave version (brave://version info)

Brave	1.9.80 Chromium: 81.0.4044.138 (Official Build) (64-bit)
Revision	8c6c7ba89cc9453625af54f11fd83179e23450fa-refs/branch-heads/4044@{#999}
OS	Windows 7 Service Pack 1 (Build 7601.24544)

Brave	1.10.87 Chromium: 83.0.4103.61 (Official Build) (64-bit)
Revision	94f915a8d7c408b09cc7352161ad592299f384d2-refs/branch-heads/4103@{#561}
OS	Ubuntu 18.04 LTS

Brave	1.12.14 Chromium: 83.0.4103.97 (Official Build) nightly (64-bit)
Revision	326d148b9655369b86498d9ecca39f63dd2bdd2d-refs/branch-heads/4103@{#657}
OS	Ubuntu 18.04 LTS

Version/Channel Information:

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

cc @brave/legacy_qa @rebron @bsclifton @mkarolin @simonhong

[bsclifton]

Duplicate of #8365