News customize 2.0 - Channel images and follow button changes

[petemill]

@aguscruiz has provided a design which uses the same icons as the mobile design for channels, both on cards and favicons.

https://www.figma.com/proto/SDcE22eeUsV2uc4dy3NwaC/Onboarding?page-id=728%3A57643&node-id=753%3A63473&viewport=-1602%2C515%2C1.41&scaling=min-zoom&starting-point-node-id=740%3A67470

https://www.figma.com/file/SDcE22eeUsV2uc4dy3NwaC/Onboarding?node-id=753%3A63473

Other changes, from @aguscruiz:

Side panel:

• the unfollow button appears on hover, not always present.
  List of sources:
• the follow button appears on hover too
• If you click follow, then the "unfollow" button remains there in case you change your mind
• There's a subtle drop-shadow on hover

[petemill]

Update: the "unfollow" button should always be visible. The "follow" button should only show on hover. This is to make it easier to glance at which results are already-following.

[fallaciousreasoning]

I think we can close this now you've fixed the follow button and I've fixed the channel cards in #15524

[kjozwiak]

The above will require 1.46.100 or higher for 1.46.x verification 👍

[stephendonner]

Verification PASSED using

Brave	1.46.100 Chromium: 107.0.5304.91 (Official Build) dev (x86_64)
Revision	3d5948960d62418160796d5831a4d2d7d6c90fa8-refs/branch-heads/5304@{#1097}
OS	macOS Version 11.7.1 (Build 20G918)

Steps:

1. installed 1.46.100
2. launched Brave
3. clicked Skip welcome tour
4. opened brave://flags
5. set brave://flags/#brave-news-v2 to Enabled
6. clicked Relaunch
7. opened a new-tab page
8. scrolled down
9. clicked on Show Brave News
10. now, clicked on Customize
11. typed gamespot
12. hovered over Follow
13. clicked on Follow
14. moused away from the Gamespot card
15. hovered over Gamespot card again
16. confirmed I saw Unfollow
17. hovered over the Unfollow button
18. clicked Unfollow

Confirmed the following various default and hover states for the Follow and Unfollow buttons and channel cards.

Follow, default	Follow, hover state	Followed state	Unfollow, card hover state	Unfollow, button hover state