CW buttons should use Brave brand style

[LaurenWags]

Description

Similar to #6398

Crypto Wallet buttons should use Brave brand styling.

Steps to Reproduce

1. Navigate to Crypto Wallets
2. Enable and confirm buttons use Brave brand style

Actual result:

Crypto wallet buttons do not use Brave brand style (some screenshots of all buttons can be seen here: #6398 (comment) )

Expected result:

Crypto wallet buttons should use Brave brand style

Reproduces how often:

easily

Brave version (brave://version info)

Brave	0.71.111 Chromium: 78.0.3904.87 (Official Build) (64-bit)
Revision	20c21f4010010f32462ea8e1d6af30cef66d48c8-refs/branch-heads/3904@{#840}
OS	macOS Version 10.13.6 (Build 17G5019)

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

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: