branded: remove Bootstrap style `@import bootstrap/scss/button-group`

Created by: gitstart-sourcegraph

Description

We depend on Bootstrap styles in our global styles a lot. But we don't plan to move forward with Bootstrap because we're working on our design system called Wildcard. To ease the transition to our styles and gain more control over visual changes, we want to move Bootstrap styles that we need into our codebase and eventually drop Bootstrap dependency.

Success Criteria

1. All highlighted imports has been removed
2. All css rules currently used from the imports are now available in style sheets

Ref

• Gitstart Task
• Sourcegraph issue