Paper
In Material Design, the physical properties of paper are translated to the screen.
The background of an application resembles the flat, opaque texture of a sheet of paper, and an application's behavior mimics paper's ability to be re-sized, shuffled, and bound together in multiple sheets.
Elevation
The elevation can be used to establish a hierarchy between other content. In practical terms, the elevation controls the size of the shadow applied to the surface. In dark mode, raising the elevation also makes the surface lighter.
The change of shade in dark mode is done by applying a semi-transparent gradient to the background-image property.
This can lead to confusion when overriding the styles of Paper, as setting just the background-color property will not affect the elevation-related shading.
To ignore the shading and set the background color that is not affected by elevation in dark mode, override the background property (or both background-color and background-image).