Fix CSS for choice elements in outline docs

[aj-stein-nist]

User Story

As an OSCAL tools developer, in order to better understand the use of choice in outline documentation, I want better layout so I can better understand hierarchical options of choices and their relationships to sibling elements that are siblings (even though they look like children).

Goals

We want to adjust the choice so, per the example below, condition and test-reference are on the same level of the hierarchy as pre-condition not indented as children of it.

Dependencies

No response

Acceptance Criteria

• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

[aj-stein-nist]

Assigning from Dave to myself as he rolled off the project. Will review backlog and consider priority and whether to include in next sprint or backlog.

[aj-stein-nist]

Talked with @david-waltermire-nist Friday. Dave still likely has some WIP code for this issue on his workstation he can get over to us on Tuesday.

[nikitawootten-nist]

I'm picking this up for the current sprint.

[nikitawootten-nist]

Below are a few options I've come up with that maintain the same indentation while clearly showing which children belong to a choice. I'm personally leaning towards option 2.

Option 1:

Deindent the choices to the same position as the other entries using a negative margin, and set a background color to convey which children belong to the choice.

Option 2:

Same as option 1, but prevent the background from overflowing to the right.

Option 3:

Add a horizontal line at the same point of indentation, conveying that the elements are not children of the previous elements while maintaining the "cascading" design.