Problem creating a custom theme

Hi, I’m trying to set up a custom theme for inverted gauge colors (low values being green, high values red)… I’ve put the following in configuration.yaml and the theme gauge_inverted appears in the theme selection dropdown when I configure a lovelace card, but nothing else happens - colors stay the same. What am I missing?

frontend:
  themes:
    gauge_inverted:
      label-badge-green: red
      label-badge-yellow: yellow
      label-badge-red: green

Thnx for helping :wink: