[UX] Fixed: Button colors are inconsistent when Basis used as admin theme

[jenlampton]

Description of the bug

We should have four distinct button colors:

• primary (blue for basis)
• secondary (white for basis)
• default (gray for basis)
• dangerous (red for basis)

Every time there is a button in the admin theme, it should be gray, unless it also has a class for primary or secondary, in which case it should take on the specific color.

Steps To Reproduce

To reproduce the behavior:

1. Switch your site to use Basis for admin theme
2. Visit the content listing
3. Edit an Article

Actual behavior

Many buttons are blue, when they should be white or gray.

Expected behavior

Only the "Save" button should be blue.

[hosef]

We also use red buttons for dangerous actions like deleting content.

[jenlampton]

Thanks @hosef, I added that to the list above (though I haven't noticed any issues with danger buttons in Basis yet...)

[hosef]

I haven't either. I just wanted to make sure it was on the list so the styles didn't get removed accidentally.

[himanshu007-creator]

HI @jenlampton , kindly review this PR. It will close this issue.
Made during the OSD

[jenlampton]

I found a small coding standards issue that needs to be resolved. Since I was doing the testing while the PR was being created, it would be best if someone else could test it. Testing can be done in the sandbox on the PR.

[himanshu007-creator]

@jenlampton Hi! Changes were made as you suggested and I have tested these changes positively.
They work as expected and now both buttons are gray. Good job @thivyaa-web-dev 🎉

[jenlampton]

Looks great, this PR is RTBC and I've adjusted the milestone so it should get into the next release!

[laryn]

Thanks to @thivyaa-web-dev for this PR, and to @jenlampton and @himanshu007-creator for testing and review! I've merged backdrop/backdrop#3668 into 1.x and 1.19.x in backdrop/backdrop#3668