title: My UI doesn't work anymore after applying Material Design
body: <p>I started learning Material Design with this video: <a href="https://www.youtube.com/watch?v=0hR2skWlb_U&amp;t=183s" rel="nofollow noreferrer">https://www.youtube.com/watch?v=0hR2skWlb_U&amp;t=183s</a></p>
  
  <p>After some changes in the styles.xml and a new added styles.xml for v21 (for backward compatibility), My UI Screen is completely black (I have to set background color on my own) and elements like buttons do not work. Check this picture:</p>
  
  <p><a href="https://i.stack.imgur.com/U1IhJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/U1IhJ.png" alt="enter image description here"></a></p>
  
  <p>The textsize was nearly invisible, I had to make it bigger. But check the buttons - they are not even buttons! Yeah I did not add constraints yet, I just want to show you what's going on.</p>
  
  <p>The xml code for the design should be fine, I just took it from another project of mine, but in case it is important here:</p>
  
  <p>activity_main.xml: </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;androidx.constraintlayout.widget.ConstraintLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background="#ffffff"
      tools:context=".MainActivity"&gt;
  
  
      &lt;Button
          android:id="@+id/button"
          android:layout_width="85dp"
          android:layout_height="64dp"
          android:text="Button"
          android:textSize="20sp"
          tools:layout_editor_absoluteX="127dp"
          tools:layout_editor_absoluteY="97dp" /&gt;
  
      &lt;Button
          android:id="@+id/button2"
          android:layout_width="124dp"
          android:layout_height="71dp"
          android:text="Button"
          android:textSize="20sp"
          tools:layout_editor_absoluteX="125dp"
          tools:layout_editor_absoluteY="223dp" /&gt;
  &lt;/androidx.constraintlayout.widget.ConstraintLayout&gt;
  </code></pre>
  
  <p>The important changes - and I think that's what has caused the error - is this: I changed the styles.xml.</p>
  
  <p>styles.xml:</p>
  
  <pre><code>&lt;resources&gt;
      &lt;!-- below api 21 --&gt;
      &lt;style name="AppMaterialTheme" parents="SuperMaterialTheme"&gt;
  
  
      &lt;/style&gt;
  
       &lt;style name="SuperMaterialTheme" parent="Theme.AppCompat.Light"&gt;
          &lt;!-- Customize your theme here. --&gt;
          &lt;!-- muss 500 tint sein --&gt;
          &lt;item name="colorPrimary"&gt;@color/colorPrimary&lt;/item&gt;
          &lt;!-- muss 700 tint sein --&gt;
          &lt;item name="colorPrimaryDark"&gt;@color/colorPrimaryDark&lt;/item&gt;
          &lt;!-- muss 200 tint sein --&gt;
          &lt;item name="colorAccent"&gt;@color/colorAccent&lt;/item&gt;
      &lt;/style&gt;
  
  &lt;/resources&gt;
  </code></pre>
  
  <p>And I added another styles.xml for phones with API 21 or above, here is the structure:</p>
  
  <p><a href="https://i.stack.imgur.com/oeWrO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oeWrO.png" alt="enter image description here"></a></p>
  
  <p>the styles.xml under values-v21 looks like this:</p>
  
  <p>values-v21/styles.xml:</p>
  
  <pre><code>&lt;resources&gt;
  
      &lt;style name="AppMaterialTheme" parents="SuperMaterialTheme"&gt;
  
      &lt;/style&gt;
  
  &lt;/resources&gt;
  </code></pre>
  
  <p>I have no idea what is going on and would be really thankful if someone can bring some light into the dark.</p>
  
  <p>Thanks for every answer!</p>