USWDS - Button group: Fix margins on nested button groups

[amyleadem]

Summary

Improved styles for nested button groups. Now, nested button groups should match the height of their parents.

• Added styles for nested button groups so that the child elements are the same height as their parents.
• Added a test story to show nested button groups.
• Updated file names in button tests to match common convention.

Breaking change

This is not a breaking change.

Related issue

Closes #5825

Related pull requests

Changelog PR

Preview link

Nested button group test story

Problem statement

Buttons in nested button groups have mismatched heights.

Solution

This PR adds styles for nested button groups so that the nested buttons are the same height as their parents.

Testing and review

1. Confirm that elements in nested button groups are the same height as each other
2. Confirm that elements in nested button groups are the same height as their parent buttons
3. Confirm the code meets standards

[mahoneycm]

Lgtm! Two non blocking comments but this works for me 👍

Testing checklist

• Confirm that elements in nested button groups are the same height as each other
• Confirm that elements in nested button groups are the same height as their parent buttons
• Confirm the code meets standards

[mejiaj]

Overall looks good. Two comments.

I tested mobile, tablet, and desktop sizes.

[mejiaj]

Is this property required? Not seeing any effect on test when disabled.

[amyleadem]

Good catch. It looks like this isn't needed anymore. I removed this in 8a926e3

[mejiaj]

The test prefix is added at the start of the filename. For example: test-usa-button-group--nested.twig.

I realize component template is hardcoded, but in the future we should avoid additional hardcoded components to allow for easier test template creation. As-is this hardcoded test template is okay.

[amyleadem]

I updated the file names in the button group /test-patterns/ directory to reflect the common naming convention for these files in 85f2945

[mejiaj]

Looks good. I tested in Chromium 125, Firefox 127, and Safari 17.4.1.

[mejiaj]

Fixed indents in df884c8.

[thisisdano]

Thank you!