Custom:canvas-gauge-card cannot change font size valuebox

According to the manual it should be able to change the fontsize of the valuebox.
However when I change the value of fontValueSize or fontValueWeight nothing happens. Only the size of the box itself changes

  - type: horizontal-stack
    cards:              
      - type: custom:canvas-gauge-card
        card_height: 125
        entity: sensor.balance_daily_power
        font_size: 1em
        fontValueSize: .5em
        fontValueWeight: bold
        shadow_height: "5%"
        gauge:
          borders: false
          height: 120
          width: 120
          highlights:
            - color: 'rgba(200, 50, 50, .3)'
              from: -11
              to: 0
            
            - color: 'rgba(0,255, 33, .3)'                
              from: 0
              to: 8
          majorTicks:
            - '-20'
            - '-15'
            - '-10'
            - '-5'
            - '0'
            - '5'
            - '10'
            - '15'
            - '20'
          maxValue: 20
          minValue: -20
          minorTicks: 2
          startAngle: 90
          strokeTicks: true
          ticksAngle: 180
          title: dagsaldo
          type: radial-gauge
          valueBox: true
          width: 220
          fontValueSize: 0.9em
          fontValueWeight: bold