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First, install archlinux-artwork
pacman -S archlinux-artwork
This will install wallpapers, logs and icons of Arch in /usr/share/archlinux. Than edit file footlogo-floaters.desktopin /usr/share/applications/screensavers:
vi /usr/share/applications/screensavers/footlogo-floaters.desktop
and change the following line Exec=floaters /usr/share/pixmaps/gnome-logo-white.svg
to two lines:#Exec=floaters /usr/share/pixmaps/gnome-logo-white.svg
Exec=floaters /usr/share/archlinux/logos/archlinux-vert-light.svg