[SOLVED] grub resolution && GNOME 3 login screen background

Hello! i'm using Mageia 5 GNOME. in Debian - Mint - Ubuntu, to change grub - terminal resolution i edit "grub" file (sudo gedit /etc/default/grub) and change lines to GRUB_CMDLINE_LINUX_DEFAULT="splash vga=792" and GRUB_GFXMODE=1024x768 , how can i change it in Mageia? there is no 'grub' file i can find.
and how can i change login screen backgroud?
sorry for my english)
and how can i change login screen backgroud?
sorry for my english)