Lovelace: Button card

hello, I would like to create a button card that changes the background of the card to me when a template sensor varies as an attribute has an entity_picture.

type: custom:button-card
name: Radio
entity: input_boolen.web_radio
styles:
card:
- background: |
[[[
return ‘’ + states[‘sensor.template_radio_prova’].attributes.entity_picture;
]]]
- background-size: cover
- background-blend-mode: screen

I am in my novice