Pipeline Graph Structural Update: Code Cleanup List: CSS Part 1

What does this MR do?

As part of #291043 (closed), this MR removes CSS no longer needed by the pipeline graph and decomposes one class into utilities.

This covers the first two items in the list; a final MR to transfer the dropdown will deal with remaining CSS.

Screenshots or Screencasts (strongly suggested)

this branch	production

Please note: Only padding changes expected

How to setup and validate locally (strongly suggested)

1. Set up a Runner.
2. Add a gitlab-ci.yml file. (I used this one, but it involves downstreams, so those need to be set up or deleted.)
3. Run pipeline.
4. Look at graph.

Does this MR meet the acceptance criteria?

Conformity

• I have self-reviewed this MR per code review guidelines.
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.

Related to #291043 (closed)