Lovelace: Show light brightness underneath the light?

I’m moving over to the Lovelace UI, but there’s something I’ve not managed to replicate from my old config.

I use Custom UI to show the light brightness underneath some lights

Example code:

    friendly_name: "Office Light"
    icon: mdi:ceiling-light
    custom_ui_state_card: state-card-custom-ui
    extra_data_template: >
      if (attributes.brightness) return Math.round(attributes.brightness / 2.55) + '%'; else return null;

Is there any way to do this with Lovelace, maybe somehow with secondary_info:?

I’m also wondering how to get custom ui greatness in lovelace

No way to do it currently without a custom card, secondary info only shows entity_id’s or last updated.

Ah, OK. Thanks.