## Description
This pull request solves the problem where the avatar component within
the document list has the same z-index value as the header component,
causing the avatar to be above the header. When two elements have the
same z-index value, the last one takes priority!
## Related Issue
Fixes#870
## Changes Made
1. Increases the value of the header's `z-index` by `10` (the current
value is `50`