core/homeassistant/components/frontend/services.yaml

# Describes the format for available frontend services

set_theme:
  name: Set theme
  description: Set a theme unless the client selected per-device theme.
  fields:
    name:
      name: Theme
      description: Name of a predefined theme
      required: true
      example: "default"
      selector:
        theme:
    mode:
      name: Mode
      description: The mode the theme is for.
      default: "light"
      selector:
        select:
          options:
            - label: "Dark"
              value: "dark"
            - label: "Light"
              value: "light"

reload_themes:
  name: Reload themes
  description: Reload themes from YAML configuration.