Create a directory ~/.config/rio/themes if it does not already exist.
Copy cyberdream.json and/or cyberdream-light.json to the directory.
Put the following config into the config.toml under ~/.config/rio.
Use default or light theme:
# ---
theme = "cyberdream"
# ---Or, follow system theme:
# ---
[adaptive-theme]
light = "cyberdream-light"
dark = "cyberdream"
# ---See also: Rio - Docs - Themes