Lovelace horizontal-stack problem

I would like to have two weather images in a horizontal stack. But they show below each other.
What am I doing wrong (newbie)

indent preformatted text by 4 spaces  - type: horizontal-stack
title: Meer weer
cards:
  - type: iframe
    url: https://embed.windy.com/embed2.html
    #aspect_ratio: 100%
  - type: picture-glance
    title: regenradar
    image:
    camera_image: camera.weer
    entities:
      - camera.weer