Thermostat Card: How to change Font Size via theme?

I would like to change the font size of the shown temperature, but I can not figure out how to do this.

Since the last update I did today, it looks like this on my Raspi Smarthomepanel:


–> The font size is to big. I even cannot change this via the Browser settings.

Now I tried to figure out, how to change this via an own theme.
As far as I understood this, it should be possible, to overwrite the setting for the font size.

So I found out, that the attribute is current-temperature-font-size: which works well for my panel, when it is set to 35px.

Now I did that:

  • in my ui-lovelace.yaml:
          - type: thermostat
            # Thermostat Bad
            name: Bad
            entity: climate.hmccrtdn_meq1559436
            theme: thermostat-smallfont
  • in my themes.yaml:
  current-temperature-font-size: '35px'

Seems to be wrong, as nothing happens. The thermostat card looks the same.
What do I wrong?