Resolve "Update the spinner component"

What does this MR do?

This MR adds the required css to the application.scss file which is needed to update the spinner component in gitlab-ui

Credit to @filipa for the css!

What are the relevant issue numbers?

Will close #20084 (closed) once this as well as the gitlab-ui spinner component has been merged.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the style guides