Settings: 4 pane layout has large right margin

When navigating through settings, settings that can lead to a four-pane layout (e.g., loan policies, due date schedules) have a large right margin which interferes with the display of the third and fourth pane.

1. On folio-snapshot as diku-admin
2. Navigate to Settings > Circulation > Loan policies > Example loan policy

Expected: four panes fill width of screen
Actual: large margin occurs when 3 panes are open or 4 panes are open

Notes: Not the same behavior as UIU-918, but perhaps related.