Card totally transparent

Is there a way to render this card totally transparent ?

Schermata 2020-11-28 alle 17.55.21

I tried in this way:

          - type: custom:stack-in-card
            style: |
              ha-card {
                font-size: 14px;
                font-family: 'Georgia';
                font-weight: normal;
                background: 'none';
                padding: 0px 0px 0px 0px;
              }
            cards:
              - type: grid
                title: Studio
                cards:

Tried also background-color: 'none'
But without success…