The sidebar style resets back to the mod's custom one when you restart the game, regardless of which style you had selected when you closed the game. This seems to only affect full restarts, as switching worlds or leaving and rejoining keeps the style you have selected.
I have not tested multiplayer but I assume the same applies, as it seems the client doesn't have any way of tracking which type you had selected while the game is closed, so it reverts back to default when the game is closed.
The sidebar style resets back to the mod's custom one when you restart the game, regardless of which style you had selected when you closed the game. This seems to only affect full restarts, as switching worlds or leaving and rejoining keeps the style you have selected.
I have not tested multiplayer but I assume the same applies, as it seems the client doesn't have any way of tracking which type you had selected while the game is closed, so it reverts back to default when the game is closed.