Improve mobile-friendliness of paid feature highlight experiment

What does this MR do?

Improves the mobile-friendliness of the Highlight Paid Features During Active Trial experiment. In order to do so, we need to make use of some gitlab-ui utility classes that do not yet exist. Since this is only an experiment, we’ve opted to add those utility classes directly to the codebase. There is a follow-up issue to move them to the gitlab-ui project as part of the experiment clean-up phase should this experiment be deemed a success.

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How to test this locally

Please follow the directions from this MR.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because it is part of an experiment and is behind a feature flag.
• [-] 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

Related to #327997 (closed)