title: How to remove the border around the toolbar?
body: <p>In my app I am using a toolbar and it seems there are borders around it that I'd like to get rid of :
  <a href="https://i.stack.imgur.com/PLJfu.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/PLJfu.jpg" alt="enter image description here"></a></p>
  
  <p>and I created it like that : 
      </p>
  
  <pre><code>&lt;android.support.design.widget.AppBarLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="@color/transparent"&gt;
  
      &lt;android.support.v7.widget.Toolbar
          android:id="@+id/toolbar"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:gravity="center"
          android:layout_gravity="center"
          android:minHeight="?attr/actionBarSize"/&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p>and I use it like that :</p>
  
  <pre><code>&lt;LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"&gt;
  
      &lt;include
          layout="@layout/app_bar_main_light"
          android:layout_width="match_parent"
          android:layout_height="wrap_content" /&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>And I never found an attribute or styling specifying what is this border.</p>