Card Mod question

Hi all. Forgive me this newbie question but I’ve always learned that the dummest questions are the once never asked :wink:
I’m trying to change the color of the battery level text in a mushroom template card with help of card_mod. This is what it looks like now:
image
and this is the code I’ve been trying:

type: horizontal-stack
cards:
  - type: custom:mushroom-template-card
    card_mod:
      style: |
        .multiline_secondary {
          color: green;
        }
    primary: Bijkeuken binnendeur
    secondary: >-
      {% if

      is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2', 'off')
      %}
        dicht
      {% elif

      is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2', 'on') %}
        open
      {% else %}
        niet open of dicht
      {% endif %}battery level: {{
      states('sensor.bijkeuken_binnendeur_battery_level_2') }}%
    icon: >-
      {% if

      is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2', 'off')
      %}
        mdi:door-closed
      {% elif

      is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2', 'on') %}
        mdi:door-open
      {% else %}
        mdi:door-open
      {% endif %}
    entity: binary_sensor.bijkeuken_binnendeur_sensor_state_any_2
    multiline_secondary: true
    icon_color: >-
      {% if is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2',
      'off') %}
        grey
      {% elif is_state('binary_sensor.bijkeuken_binnendeur_sensor_state_any_2',
      'on') %}
        brown
      {% else %}
        mdi:window-open-variant
      {% endif %}

My question mainly is: how do I figure out which CSS element to put after style: |
I have been investigating with devTools and cannot figure out what I am doing wrong: