Based on the vim theme made by sainnhe .
Download the theme(s) and put them in the kitty theme folder.
The themes will be available when running kitty +kitten themes.
The Everforest themes for (neo)vim can be found here https://github.com/sainnhe/everforest
I'd recommend Tmuxline to automatically create a Tmux theme.
Create a snapshot and add it to your tmux conf file to persist the theme on restarts.
Append this line set -wg mode-style bg=*selection_background,fg=**selection_foreground to make selections follow the theme in copy mode.
(*selection_background = eg. #503946)
(**selection_foreground = eg. #9da9a0)