How to remove MaterialCardView borders

I'm using this layout

<android.support.design.card.MaterialCardView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:innerRadius="0dp"
    android:shape="ring"
    android:thicknessRatio="0"
    app:cardCornerRadius="24dp"
    card_view:cardElevation="0dp"
    card_view:cardMaxElevation="0dp">
  <ImageView
      android:id="@+id/close_button"
      android:layout_width="48dp"
      android:layout_height="48dp"
      android:layout_gravity="top|end"
      android:padding="@dimen/account_menu_close_button_padding"
      android:alpha="0"
      app:srcCompat="@drawable/quantum_gm_ic_close_vd_theme_24"
      />
</android.support.design.card.MaterialCardView>

but I get a cardView with tiny border

How can I remove this border and make the cardview transparent?

I saw this similar post, but it gives no answer

Just use the MaterialCard included in the Material Components library that extends the androidx.cardview.widget.CardView (the old CardView included in support library).

You can change the border using the app:strokeWidth attribute. The default value is 0.

<com.google.android.material.card.MaterialCardView
    app:strokeColor="@color/..."
    app:strokeWidth="xxdp"
    ../>