Add source button text is unreadable on hover state

[stephendonner]

Description

Add source button text is unreadable on hover state

Steps to Reproduce

1. new profile
2. launch Brave
3. open a new-tab page
4. opt in to Brave News
5. click on Customize
6. click on Brave News
7. hover over the Add source button
8. try to read it

Actual result:

It's unreadable: white-on-white text and background.

Expected result:

Button text isn't obscured by color change; remains readable upon hover

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.36.60 Chromium: 97.0.4692.99 (Official Build) nightly (64-bit)
Revision	d740da257583289dbebd2eb37e8668928fac5ead-refs/branch-heads/4692@{#1461}
OS	Windows 10 Version 20H2 (Build 19042.1466)

cc @petemill @mattmcalister @srirambv

[stephendonner]

Verified PASSED using

Brave	1.38.7 Chromium: 99.0.4844.45 (Official Build) nightly (x86_64)
Revision	edbc0b8343c7b10fddb0e1b4efb280b0f6e38cab-refs/branch-heads/4844@{#788}
OS	macOS Version 12.3 (Build 21E5222a)

Confirmed default, hover, and clicked states, using light and dark themes.

example	example

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.36.115 Chromium: 99.0.4844.51 (Official Build) (64-bit)
-- | --
Revision | d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS | Windows 10 Version 21H2 (Build 19044.1586)

• Verified the STR mentioned in the description and enured mouse hover text is in readable format

Light mode	Dark mode