Search Engine selection dialog has incorrect radio button color when using dark theme

[LaurenWags]

Description

When using dark theme, the radio button color on the Search Engine selection dialog box is the wrong color, it's Chrome blue instead of a blurple color. See internal discussion here.

Light theme color for radio button appears to be fine.

Found when testing #49215 but issue is present in versions before this change.

Steps to reproduce

1. Be using dark theme
2. Navigate to brave://settings/search/defaultSearch or brave://settings/search/privateSearch
3. Note radio button color

For @brave/qa-team when verifying this, check that light theme still looks fine.

Actual result

Radio button color is Chrome blue, not Brave blurple (light blurple due to dark theme)

1.82.x	1.84.x

Expected result

Per discussion in slack, the radio button should be the same color as the "Set as Default" button. This appears to be working for Light theme:

Reproduces how often

Easily reproduced

Brave version (brave://version info)

1.82.170 (current release), 1.83.99 (Beta), 1.84.76 (Nightly)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

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

Miscellaneous information

cc @rebron @aguscruiz