title: Can't remove "shadow" from unelevated transparent FloatingActionButton
body: <p>After spending multiple hours researching this problem, I decided to ask instead of wasting more time on such a (seemingly) easy task.</p>
  
  <p>I'm trying to implement a FloatingActionButton with transparent background and no broder, to show just a custom icon. I know that the material design discourages it, but I need to do it this way.</p>
  
  <p>The problem I face is that there is a shadow showing, which I don't want.
  Since I set elevation to 0dp I don't know how it got there and thus how I can remove it.</p>
  
  <p><a href="https://i.stack.imgur.com/83yKY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/83yKY.png" alt="FAB with background"></a>
  <a href="https://i.stack.imgur.com/cTezx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cTezx.png" alt="FAB without background but with shadow"></a></p>
  
  <p>Here is the code for the fragment containing the FAB:</p>
  
  <pre><code>&lt;android.support.design.widget.CoordinatorLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:id="@+id/fragment_layout"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="@drawable/bg_sample"
  android:elevation="0dp"
  android:fitsSystemWindows="true"&gt;
  
      &lt;android.support.v7.widget.RecyclerView
          android:id="@+id/fragment_grid"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:fitsSystemWindows="true"
          android:gravity="center"
          android:padding="10dp"
          android:stretchMode="columnWidth"
          android:verticalSpacing="25dp"/&gt;
  
      &lt;android.support.design.widget.FloatingActionButton
          android:id="@+id/fab"
          style="@style/AppTheme"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="bottom|center"
          android:layout_marginBottom="@dimen/activity_vertical_margin"
          android:adjustViewBounds="true"
          android:elevation="0dp"
          android:fitsSystemWindows="true"
          android:scaleType="fitCenter"
          app:borderWidth="0dp"
          app:fabSize="normal"
          app:layout_anchorGravity="bottom|center"
          app:layout_behavior="ScrollAwareFABBehavior"
          /&gt;
  
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p>Here is my AppTheme:</p>
  
  <pre><code>&lt;style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar"&gt;
      &lt;item name="colorPrimary"&gt;@color/colorPrimary&lt;/item&gt;
      &lt;item name="colorPrimaryDark"&gt;@color/colorPrimaryDark&lt;/item&gt;
      &lt;item name="colorAccent"&gt;@color/colorAccent&lt;/item&gt;
      &lt;item name="android:fitsSystemWindows"&gt;true&lt;/item&gt;
      &lt;item name="android:spotShadowAlpha"&gt;0&lt;/item&gt;
      &lt;item name="android:shadowRadius"&gt;0&lt;/item&gt;
      &lt;item name="android:ambientShadowAlpha"&gt;0&lt;/item&gt;
      &lt;item name="selectableItemBackgroundBorderless"&gt;@null&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p>The onCreateView of the Fragment in which I set the transperancy:</p>
  
  <pre><code>@Override
  public final View onCreateView(final LayoutInflater inflater, final ViewGroup container,
                                 final Bundle savedInstanceState) {
      // initialize variables
      View view = inflater.inflate(R.layout.fragment_desk, container, false);
  
      coordinatorLayout = (CoordinatorLayout) view.findViewById(R.id.fragment_layout);
      fab = (FloatingActionButton) coordinatorLayout.findViewById(R.id.fab);
      fab.getBackground().setColorFilter(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
  
      return view;
  }
  </code></pre>
  
  <p><strong>TL;DR: How can I remove the shadow shown in the second picture?</strong></p>
  
  <p>EDIT: 
  It seems, that this problem is linked to the fab size. 
  I set design_fab_size_normal to 200 just to see, what it does. Turns out it doesn't affect my icon size but the size of the shadow.</p>
  
  <p><a href="https://i.stack.imgur.com/Ipkk4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ipkk4.png" alt="FAB size increased to 200 showing icon"></a></p>
  
  <p>Here is the dimens.xml:</p>
  
  <pre><code>&lt;resources xmlns:tools="http://schemas.android.com/tools"&gt;
      &lt;dimen name="design_fab_image_size" tools:override="true"&gt;64dp&lt;/dimen&gt;
      &lt;dimen name="design_fab_size_normal" tools:override="true"&gt;200dp&lt;/dimen&gt;
  &lt;/resources&gt;
  </code></pre>