Paper
No Material Design, as propriedades físicas de um papel são traduzidas para a tela.
O fundo de uma aplicação se assemelha a textura lisa e opaca de uma folha de papel e o comportamento de uma aplicação imita a habilidade do papel de ser redimensionado, embaralhado e amontoado em várias folhas.
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).