Restyle changes header & file tree

Issue: #118442 (closed)

What does this MR do?

Restyle changes header & file tree. This is part of our initiative of design for zen code review.

Testing Case

1. Find a merge request that contains changes
2. Go to Merge Request > Changes Tab

• With File tree shown, it looks like this:

Note

• The change status text will either be: Modified, Added, Deleted
• The search will actually be lower p to reflect the actual command instead of capital P

• With File tree collapsed, it looks like this:

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #118442 (closed)