Remove border from expander-card and multiple-row-card

I am trying to remove the borders since days without success.
It is the thin grey border within the dotted red border:

HA border removal

I experimented with card_mod but no success (but I can control
the red dotted borders ;- )

This is my yaml:

theme: minimalist-mobile
type: custom:mod-card
style: |
  ha-card {
    border: 10px dotted red;
    padding: 0px 0px 0px !important;
    color: grey !important;
    background-color: ;
    font-size: ;
    background: none;
    box-shadow: none;
    ha-card-box-shadow: none
  }
card:
  type: custom:expander-card
  gap: 0.6em
  padding: 1em
  clear: false
  clear-children: false
  title: Expander
  overlay-margin: 2em
  child-padding: 0em
  button-background: transparent
  expanded: true
  title-card:
    type: custom:mod-card
    style: |
      ha-card {
        border: 10px dotted red !important;
        padding: 0px 0px 0px !important;
        color: red !important;
        background-color: ;
        font-size: ;
      }
    card:
      type: entities
      entities:
        - entity: climate.1_s_gth
          type: custom:multiple-entity-row
          name: Ost / West
          icon: mdi:heating-coil
          show_state: false
          secondary_info: last-changed
          entities:
            - type: attribute
              name: Soll
              entity: climate.1_s_gth
              attribute: temperature
            - type: attribute
              name: Ist
              entity: climate.1_s_gth
              attribute: current_temperature
            - type: attribute
              name: Batterie
              entity: binary_sensor.1_s_gth_battery_low
  cards:
    - type: custom:mod-card
      style: |
        ha-card {
          border: 10px dotted red !important;
          padding: 0px 0px 0px !important;
          color: red !important;
          background-color: ;
          font-size: ;
        }
      card:
        type: entities
        entities:
          - entity: climate.1_s_th_e
            type: custom:multiple-entity-row
            name: Ost
            icon: mdi:heating-coil
            show_state: false
            secondary_info: last-changed
            entities:
              - type: attribute
                name: Soll
                entity: climate.1_s_th_e
                attribute: temperature
              - type: attribute
                name: Ist
                entity: climate.1_s_th_e
                attribute: current_temperature
              - type: attribute
                name: Batterie
                entity: binary_sensor.1_s_th_e_battery_low
          - entity: climate.1_s_th_w
            type: custom:multiple-entity-row
            name: West
            icon: mdi:heating-coil
            show_state: false
            secondary_info: last-changed
            entities:
              - type: attribute
                name: Soll
                entity: climate.1_s_th_w
                attribute: temperature
              - type: attribute
                name: Ist
                entity: climate.1_s_th_w
                attribute: current_temperature
              - type: attribute
                name: Batterie
                entity: binary_sensor.1_s_th_w_battery_low

Any ideas?

BR,
Ypo

Thanks, for the referal. I indeed found a solution there (post was just 6 min old)

https://community.home-assistant.io/t/card-mod-add-css-styles-to-any-lovelace-card/120744/7872?u=ypoosn

--ha-card-border-width: 0;

did the trick.

BR,

Ypo