[Bug](greenhouse): Demo banner causes layout gap between main content and side navigation

[ArtieReus]

Description

When the demo banner is displayed, using the demo organisation, it pushes the main content downward but does not affect the side navigation in the same way. As a result, a visible white gap appears between the main content area and the side navigation.

Steps to Reproduce

1. http://localhost:8000/demo/alerts-demo/alerts
2. See the gap scrolling to the bottom of the page

Expected Behavior

Side navigation and main content aligned.

Screenshots