Filter overlay hides under table header

[davazlan]

Describe the bug
On a datagrid with fixed header, if I click on filter, the overlay hides partially under the header.

To Reproduce
Steps to reproduce the behavior:

1. Create a datagrid
2. Set it to fixed (Fixed="FixedMode.All")
3. Set at least one column to CanFilter="true"
4. Click on the filter

Screenshot:

Environment

• Blazority Version: 0.10.0
• .NET Core Version: 5.0
• Browser: Chrome, Edge