Improve the IA and styling of the Success screen in the Static Site Editor

What does this MR do?

It re-designs the success message displayed after saving changes in the Static Site Editor.

How to test

• Open the Static Site Editor in your local environment, you can use this example URL
• Click the submit changes button.
• You will see the new Success screen.

Screenshots

Before	After	Mobile (after)

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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