grub-install /dev/XXX

grub-mkconfig -o /boot/grub/grub.cfg

after updating kernel dont forget to run

grub-mkconfig -o /boot/grub/grub.cfg

splashscreen section GRUB_PRELOAD_MODULES=“all_video”

GRUB_BACKGROUND=/boot/grub/themes/slackware/background.png

edit /etc/default/grub and add

cp /usr/share/grub/dejavusansmono.pf2 /boot/grub/fonts/