title: Android CardView cardElevation and shadow is not working
body: <p>I have this set of Cards using CardView inside an activity.</p>
  
  <p>When running the app, I get this not expected cardview : no elevation, no shadow...</p>
  
  <p><strong>Result on Android 7 device :</strong> </p>
  
  <p><a href="https://i.stack.imgur.com/4eXth.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4eXth.png" alt="Android 7"></a></p>
  
  <p>Code</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.v7.widget.CardView
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:card_view="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_gravity="center"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      card_view:cardCornerRadius="4dp"
      card_view:cardElevation="4dp"
      card_view:cardUseCompatPadding="true"
      android:layout_margin="8dp"
      android:gravity="center_horizontal"
      android:id="@+id/card_view"
      android:padding="10dp"
      android:layout_centerHorizontal="true"
      card_view:cardBackgroundColor="@color/main_color_grey_800"&gt;
  
      &lt;LinearLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:layout_gravity="center"
          android:orientation="vertical"&gt;
  
          &lt;ImageView
              android:id="@+id/image"
              android:layout_width="match_parent"
              android:layout_height="350.0dp"
              android:scaleType="centerCrop"
               /&gt;
  
          &lt;TextView
              android:id="@+id/title"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:background="@android:color/white"
              android:padding="15.0dp"
              android:textColor="@android:color/black"
              android:textSize="16.0sp"
              android:text="@string/LoremText" /&gt;
  
          &lt;TextView
              android:id="@+id/desc"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:background="@android:color/white"
              android:padding="15.0dp"
              android:textColor="@android:color/black"
              android:textSize="12.0sp"
              android:textAlignment="center"
              android:text="@string/LoremText" /&gt;
  
          &lt;LinearLayout
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:gravity="end"
              android:orientation="horizontal"
              android:paddingTop="10.0dip"&gt;
  
              &lt;Button
                  android:id="@+id/answer_1"
                  android:layout_width="0px"
                  android:layout_height="50.0dip"
                  android:text="@string/Maybe"
                  android:textColor="@color/white"
                  android:background="@color/cpb_red"
                  android:textSize="14sp"
                  style="@style/DBTheme.Button.Orange"
                  android:textStyle="bold"
                  android:layout_weight="1"
                  tools:ignore="ButtonStyle"
                  android:visibility="gone" /&gt;
  
              &lt;Button
                  android:id="@+id/answer_2"
                  style="@style/DBTheme.Button.Orange"
                  android:layout_width="0px"
                  android:layout_height="50.0dip"
                  android:text="@string/yes_button"
                  android:textColor="@android:color/white"
                  android:textSize="14sp"
                  android:textStyle="bold"
                  android:background="@color/cpb_red"
                  android:layout_weight="1"
                  android:visibility="gone" /&gt;
              &lt;Button
                  android:id="@+id/answer_3"
                  style="@style/DBTheme.Button.Orange"
                  android:layout_width="0px"
                  android:layout_height="50.0dip"
                  android:layout_weight="1.0"
                  android:textStyle="bold"
                  android:text="@string/no_button"
                  android:textColor="@color/white"
                  android:background="@color/cpb_red"
                  android:textSize="14sp"
                  android:visibility="gone" /&gt;
          &lt;/LinearLayout&gt;
      &lt;/LinearLayout&gt;
  
      &lt;View
          android:layout_width="match_parent"
          android:layout_height="4.0dp"
          android:background="@drawable/shadow" /&gt;
  &lt;/android.support.v7.widget.CardView&gt;
  </code></pre>
  
  <p>Any ideas on how to solve this ? Thanks :)</p>