Black theme uses black background and window

app/src/main/res/layout-v21/task_adapter_row_simple.xml

@@ -16,4 +16,9 @@
 
   <include layout="@layout/task_adapter_row_body"/>
 
+  <View
+    style="@style/horizontal_divider"
+    android:visibility="?attr/horizontal_divider"
+    android:layout_gravity="bottom" />
+
 </androidx.cardview.widget.CardView>

app/src/main/res/layout/task_adapter_row_simple.xml

@@ -3,7 +3,8 @@
   android:id="@+id/row"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
-  android:orientation="vertical">
+  android:orientation="vertical"
+  android:background="?android:colorBackground">
 
   <include layout="@layout/task_adapter_row_body"/>
 

app/src/main/res/values/attrs.xml

@@ -15,6 +15,7 @@
   <attr format="reference" name="materialButtonStroke"/>
   <attr format="reference" name="weekdayButtonBackground"/>
   <attr format="reference" name="weekdayButtonText"/>
+  <attr format="integer" name="horizontal_divider"/>
 
   <declare-styleable name="TimePreference">
     <attr format="string" name="summary"/>

app/src/main/res/values/theme.xml

@@ -29,6 +29,7 @@
     <item name="materialButtonStroke">@color/mtrl_btn_stroke_color_selector</item>
     <item name="weekdayButtonBackground">?attr/colorPrimary</item>
     <item name="weekdayButtonText">?attr/colorOnPrimary</item>
+    <item name="horizontal_divider">2</item> <!-- View.GONE -->
   </style>
 
   <style name="Tasks" parent="TasksBase"/>
@@ -40,8 +41,9 @@
   <style name="TasksDialog" parent="DayNightDialog"/>
 
   <style name="ThemeBlack" parent="Tasks">
-    <item name="android:windowBackground">@color/grey_900</item>
+    <item name="android:windowBackground">@android:color/black</item>
     <item name="android:colorBackground">@android:color/black</item>
+    <item name="horizontal_divider">0</item> <!-- View.VISIBLE -->
   </style>
 
   <style name="Wallpaper" parent="Tasks">