[NathanZlion]

Description

With column groups and borderless/embedded/full-page tables, the last leaf column of a group had its resize divider misaligned by 12px when a standalone column with rowspan=2 followed the group.

The resizer wrapper uses inset-inline-end: -12px by default to straddle the cell boundary. A CSS th:last-child rule reset it to 0 for borderless tables to prevent overflow at the table edge. With column groups, a standalone column with rowspan=2 is rendered only in the group header row, so the leaf row's th:last-child becomes the group's last leaf column — not the table's rightmost column. The CSS rule incorrectly pulled that column's resizer 12px inward.

Replaced the th:last-child CSS rule with the existing JS-driven .is-last class, which identifies the rightmost column via colIndex + colSpan === totalColumns regardless of DOM row structure.

Related links, issue #: AWSUI-62435

How has this been tested?

• Opened the column-groups dev page with variant=borderless, single-level groups preset
• Verified the resize divider on the last leaf column of each group aligns with the group header divider
• Verified the rightmost column (Cost) still has its resizer pulled inward to prevent table overflow
• tsc --noEmit passes

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates. N/A — CSS-only fix, no API change.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md. Yes, no public API changes.
• Changes do not include unsupported browser features, see CONTRIBUTING.md. Yes, only moved an existing CSS rule.
• Changes were manually tested for accessibility, see accessibility guidelines. N/A — visual positioning only, no accessibility impact.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function. N/A

Testing

• Changes are covered with new/existing unit tests? The existing resizable-columns tests cover the .is-last class behavior.
• Changes are covered with new/existing integration tests? N/A

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.76%. Comparing base (8a3001d) to head (f00f7cf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5224   +/-   ##
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  Coverage   97.76%   97.76%           
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  Files        1003     1003           
  Lines       32572    32572           
  Branches    12109    12110    +1     
=======================================
  Hits        31843    31843           
+ Misses        723      684   -39     
- Partials        6       45   +39     

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[Copilot]

🟡 Changes recommended

The selector change leaves the last classic-mode resize handle at a negative inset, extending it beyond the table edge and potentially causing horizontal overflow.

1 open issue

• Reset the last classic table resizer wrapper · New

What changed in this PR

Fixes resize-divider alignment in Cloudscape tables with column groups by using logical column position rather than DOM row order.

Changes:

• Removes the th:last-child wrapper-positioning rule.
• Moves the inset reset to the existing JavaScript-driven .is-last selector for visual-refresh borderless tables.

File	Description
src/​table/​resizer/​styles.scss	Uses .is-last to position the final column’s resize wrapper.

_{Review effort: Balanced}