Steps to Reproduce

1. import group.xlsx
2. check group related UI

Current Result

1. plus icon is obviously not vertically centered-aligned
2. row headers look like they all have missing left borders

Expected Result

can follow Excel design. See group.css

1. suggest 2 options

• option1: add left borders on all row headers.
• 
• option2: we can apply a background color (gray) on the left group area, it makes row headers look like no borders. If we add a background, it needs to make group conn