Grey background

[WattageGuy]

How to remove grey background from gauge card? See picture:

  - type: custom:gauge-card
    entity: sensor.power_fagelsangsvagen_28
    needle: false
    min: 0
    max: 3000
    severity:
      green: 0
      yellow: 600
      red: 1800
    title: Nuvarande elförbrukning
    card_mod:
      style: |
        ha-card {
          border-radius: 0px;
           }