Card does not show up in a picture-element card.

Card does not show up in a picture-element card.
No error is shown.

type: vertical-stack
cards:
- type: picture-elements
image: /local/images/zaptec-go-front-white.png
elements:
- type: custom:flex-horseshoe-card
entities:
- entity: sensor.zaptec_home_temperature
attribute: temperature
decimals: 1
unit: °C
area: De Maan
show:
horseshoe_style: lineargradient
layout:
states:
- id: 0
entity_index: 0
xpos: 50
ypos: 60
styles:
- font-size: 3.5em;
- opacity: 0.8;
horseshoe_scale:
min: -10
max: 40
color_stops:
'10': red
'18': blue