Fonts & Colors - NULL field background color

I have changed the fonts and colors of SQL Server to emulate a dark mode. The only problem I have now is that the NULL field is unreadable.

See this screenshot for an illustration:

The regular fields are white text with black background. I did this by changing Fonts & Colors > Grid Results > Text. How do I change the background of the NULL field (3rd row)? The only option in Grid Results is "Text".

I am using SQL Server Management Studio 20.