Why?
The previous design is a bit confusing since the built-in palettes of g:gruvbox_material_palette will only change the foreground colors, while the background colors are controlled by g:gruvbox_material_background.
To make the design more reasonable and match the design of my other color schemes, I decide to split this option.
Sincere apologies for the inconvenience caused.
How to update my vimrc?
If g:gruvbox_material_palette is set to a string, for example 'material', simply replace this option with g:gruvbox_material_foreground.
let g:gruvbox_material_foreground = 'material'
If g:gruvbox_material_palette is set to a dictionary, replace it with g:gruvbox_material_colors_override
let g:gruvbox_material_colors_override = {'bg0': ['#1d2021', '234'], 'bg2': ['#282828', '235']}