Positioning Titles on Lovelace Card

I’ve created a dashboard that has the following view;

Screenshot 2023-04-11 171730

I’d like to replace the headings, — Christmas Tree —, that appear over the first two columns with one heading that spans the two columns. I’ve tried various card layouts but cannot figure out how to achieve what I want. I’m using a combination of generic, mushroom and custom cards to achieve the layout. My current code follows;

square: false
columns: 1
type: grid
cards:
  - type: custom:mushroom-title-card
    title: Seasonal Lighting
  - square: false
    type: grid
    cards:
      - type: custom:text-divider-row
        text: Christmas Tree
      - type: custom:text-divider-row
        text: Christmas Tree
      - type: custom:text-divider-row
        text: Village
    columns: 3
  - square: false
    columns: 3
    type: grid
    cards:
      - type: vertical-stack
        cards:
          - type: custom:mushroom-entity-card
            entity: switch.christmas_tree_left
            layout: vertical
            name: Left
            tap_action:
              action: toggle
          - type: custom:mushroom-entity-card
            entity: switch.christmas_tree_left_led
            name: LED
            layout: vertical
            primary_info: name
            tap_action:
              action: toggle
            hold_action:
              action: none
            double_tap_action:
              action: none
      - type: vertical-stack
        cards:
          - type: custom:mushroom-entity-card
            entity: switch.christmas_tree_right
            layout: vertical
            name: Right
            tap_action:
              action: toggle
          - type: custom:mushroom-entity-card
            entity: switch.christmas_tree_right_led
            name: LED
            layout: vertical
            primary_info: name
            tap_action:
              action: toggle
            hold_action:
              action: none
            double_tap_action:
              action: none
      - type: vertical-stack
        cards:
          - type: custom:mushroom-entity-card
            fill_container: false
            layout: vertical
            name: Village
            primary_info: name
            entity: switch.christmas_village
            tap_action:
              action: toggle

What do I need to change/add in order to place a single title over the left most two columns?

Please Note: the entities used in the Dashboard view are unplugged and stored away with the Christmas Decorations thus the reason they’re showing unavailable.