Add CSS-class to card depending on entity state

Configuration Frontend
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1

I’m looking for a way to add a class (“is_active”) to a card if the entity state is on. I’ve managed to create conditional styles using jinja and card_mod, but using the same syntax to print a class-name I’ve failed to to do - probably because my non-existing jinja-skills. Is this possible?

    type: horizontal-stack
    cards:
      - type: custom:mushroom-entity-card
        layout: vertical
        entity: binary_sensor.leak_sensors
        icon: mdi:water-off-outline
        name: Leak sensors
        card_mod:
          class: {% if states('binary_sensor.leak_sensors'), 'on'} is_active {% else %} {% endif %}
     [...]
2

Not possible to use templates to define a class.
FR