First clone the repository:
git clone https://github.com/Eayu/sddm-theme-clairvoyance
Then move it to the sddm-themes directory:
sudo mv sddm-theme-clairvoyance /usr/share/sddm/themes/clairvoyance
Then set the current theme to clairvoyance in sddm.conf:
sudo vim /etc/sddm.conf
and set "Current" equal to "clairvoyance" (no speech marks).
Click the image to see the video:
I shamelessly stole the power icons (shutdown restart etc.) from https://github.com/Match-Yang/sddm-deepin .