Custom swipe card - How to tame the Image size when used in a custom layout card?

Hello there,
I made a simple CSS Grid:

    type: custom:grid-layout
    icon: mdi:grid
    layout:
      grid-template-columns: 30% auto 30%
      grid-template-rows: auto
      grid-template-areas: |
        "header header header"
        "messages messages messages"
        "left middle right"
        " footer footer footer"
      mediaquery:
        '(orientation: portrait)':
          grid-template-columns: 50% 50%
          grid-template-rows: auto
          grid-template-areas: |
            "header header"
            "messages messages"
            "middle middle"
            "left right"
            "footer footer"

I wnat to put a custom:swipe-card in the grid area called “middle”. This swipe card should display picture cards / picture element cards of my rooms.

card:
      type: custom:swipe-card
      cards:
        - type: picture
          image: /local/images/kleinesWZ.webp
        - type: picture
          image: /local/images/grossesWZ.webp
 view_layout:
          grid-area: middle

If I try this, the images grow above any limits. What I’m doing wrong here?