title: BottomSheetDialogFragment header layout background transparent not working
body: <p>I have created a BottomSheetFragment. 
  Everything is fine except the header of the bottom sheet which is not getting transparent.Is there any way to make the background transparent as like as normal bottomsheetFragment works. 
  I tried by setting the parent background transparent but it is not working at all. </p>
  
  <pre><code>    &lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:id="@+id/layoutContainer"
      android:background="@android:color/transparent"&gt;
      &lt;RelativeLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:id="@+id/immediateParent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toTopOf="parent"&gt;
          &lt;LinearLayout
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"&gt;
              &lt;View
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content" /&gt;
              &lt;LinearLayout
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                 &gt;
                  &lt;LinearLayout
                      android:layout_width="match_parent"
                      android:layout_height="match_parent"
                      android:orientation="vertical"
                      &gt;
  
                      &lt;android.support.v4.widget.NestedScrollView
                          android:layout_width="match_parent"
                          android:layout_height="wrap_content"&gt;
                      &lt;/android.support.v4.widget.NestedScrollView&gt;
                  &lt;/LinearLayout&gt;
              &lt;/LinearLayout&gt;
          &lt;/LinearLayout&gt;
          &lt;com.makeramen.roundedimageview.RoundedImageView xmlns:app="http://schemas.android.com/apk/res-auto"
              android:id="@+id/imageView"
              android:layout_width="@dimen/hundrad_twenty"
              android:layout_height="@dimen/hundrad_twenty"
              android:layout_centerHorizontal="true"
              android:layout_marginTop="@dimen/sixty"
              app:riv_border_color="@color/transparent"
              app:riv_corner_radius="@dimen/twenty"
              app:riv_mutate_background="true"
              app:riv_oval="false" /&gt;
          &lt;ImageView
              android:layout_width="@dimen/thirty"
              android:layout_height="@dimen/thirty"
              android:layout_alignParentRight="true"
              android:layout_marginTop="@dimen/hundred_fifty"
              android:layout_marginRight="100dp"/&gt;
      &lt;/RelativeLayout&gt;
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>I have tired this.</p>
  
  <pre><code>ConstraintLayout layoutContainer;
  RelativeLayout immediateParent;
  
  @Nullable
  @Override
  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
      View view = null;
      view = inflater.inflate(R.layout.bottom_sheet_dialog, container);
      ButterKnife.bind(this, view);
      //parent layout transparent not working
      layoutContainer.setBackground(getResources().getDrawable(R.color.transparent));
  
      immediateParent.setBackground(getResources().getDrawable(R.color.transparent));
     //view transparent 
      view.setBackgroundColor(getResources().getColor(R.color.transparent));
      return view;
  }
  </code></pre>