Let the background color of the previews can be adapted by different wallpapers.

Remove the hardcoded background colors and let the background colors respect the theme's android:colorBackground attribute.

PS: Need to follow the steps in go/usingmonet to let the background color can change with the wallpapers.

Screenshot:
https://screenshot.googleplex.com/3K5W5BGG2tFBxnb.png

Bug: 173549815
Change-Id: I090fa9eb2303c78959f44649cfb28d1346dcf551
diff --git a/res/layout/fragment_custom_theme_name.xml b/res/layout/fragment_custom_theme_name.xml
index 532e904..98edd29 100644
--- a/res/layout/fragment_custom_theme_name.xml
+++ b/res/layout/fragment_custom_theme_name.xml
@@ -19,8 +19,7 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:orientation="vertical"
-    android:background="?android:colorPrimary">
+    android:orientation="vertical">
     <include layout="@layout/section_header"/>
 
     <androidx.constraintlayout.widget.ConstraintLayout
@@ -34,7 +33,6 @@
             android:paddingTop="@dimen/preview_content_padding_top"
             android:paddingBottom="@dimen/preview_content_padding_bottom"
             android:clipToPadding="false"
-            android:background="@color/fullscreen_preview_background"
             app:layout_constrainedHeight="true"
             app:layout_constraintBottom_toTopOf="@+id/component_scroll_view"
             app:layout_constraintEnd_toEndOf="parent"
@@ -51,6 +49,7 @@
                 android:id="@+id/component_scroll_view"
                 android:layout_width="match_parent"
                 android:layout_height="0dp"
+                android:background="?android:colorPrimary"
                 app:layout_constraintEnd_toEndOf="parent"
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintTop_toBottomOf="@+id/component_preview_container"
diff --git a/res/layout/fragment_grid_full_preview.xml b/res/layout/fragment_grid_full_preview.xml
index d39be36..b1a0ca3 100644
--- a/res/layout/fragment_grid_full_preview.xml
+++ b/res/layout/fragment_grid_full_preview.xml
@@ -28,8 +28,7 @@
         android:layout_weight="1"
         android:paddingTop="@dimen/full_preview_page_default_padding_top"
         android:paddingBottom="@dimen/full_preview_page_default_padding_bottom"
-        android:clipToPadding="false"
-        android:background="@color/fullscreen_preview_background">
+        android:clipToPadding="false">
 
         <include layout="@layout/grid_preview_card"/>
     </FrameLayout>
diff --git a/res/layout/fragment_grid_picker.xml b/res/layout/fragment_grid_picker.xml
index 84c8163..99fb04c 100644
--- a/res/layout/fragment_grid_picker.xml
+++ b/res/layout/fragment_grid_picker.xml
@@ -19,8 +19,7 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:orientation="vertical"
-    android:background="?android:colorPrimary">
+    android:orientation="vertical">
     <include layout="@layout/section_header"/>
 
     <FrameLayout
@@ -38,7 +37,6 @@
                 android:layout_height="0dp"
                 android:paddingTop="@dimen/preview_content_padding_top"
                 android:paddingBottom="@dimen/preview_content_padding_bottom"
-                android:background="@color/preview_pager_background"
                 android:clipToPadding="false"
                 app:layout_constrainedHeight="true"
                 app:layout_constraintStart_toStartOf="parent"
@@ -55,6 +53,7 @@
                 android:id="@+id/options_title"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
+                android:background="?android:colorPrimary"
                 android:gravity="center"
                 android:paddingVertical="18dp"
                 android:lineHeight="24dp"
@@ -70,6 +69,7 @@
                 android:id="@+id/options_container"
                 android:layout_width="match_parent"
                 android:layout_height="0dp"
+                android:background="?android:colorPrimary"
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintEnd_toEndOf="parent"
                 app:layout_constraintTop_toBottomOf="@id/options_title"
diff --git a/res/layout/fragment_theme_full_preview.xml b/res/layout/fragment_theme_full_preview.xml
index 008a795..762af07 100644
--- a/res/layout/fragment_theme_full_preview.xml
+++ b/res/layout/fragment_theme_full_preview.xml
@@ -28,8 +28,7 @@
         android:layout_weight="1"
         android:paddingTop="@dimen/full_preview_page_default_padding_top"
         android:paddingBottom="@dimen/full_preview_page_default_padding_bottom"
-        android:clipToPadding="false"
-        android:background="@color/fullscreen_preview_background">
+        android:clipToPadding="false">
 
         <include layout="@layout/theme_preview_card"/>
     </FrameLayout>
diff --git a/res/layout/fragment_theme_picker.xml b/res/layout/fragment_theme_picker.xml
index 2e3a6bb..893be46 100644
--- a/res/layout/fragment_theme_picker.xml
+++ b/res/layout/fragment_theme_picker.xml
@@ -18,8 +18,7 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:orientation="vertical"
-    android:background="?android:colorPrimary">
+    android:orientation="vertical">
     <include layout="@layout/section_header"/>
 
     <FrameLayout
@@ -36,7 +35,6 @@
                 android:layout_height="0dp"
                 android:paddingTop="@dimen/preview_content_padding_top"
                 android:paddingBottom="@dimen/preview_content_padding_bottom"
-                android:background="@color/preview_pager_background"
                 android:clipToPadding="false"
                 app:layout_constrainedHeight="true"
                 app:layout_constraintStart_toStartOf="parent"
@@ -55,6 +53,7 @@
                 android:layout_height="0dp"
                 android:layout_gravity="bottom|center_horizontal"
                 android:layout_marginTop="10dp"
+                android:background="?android:colorPrimary"
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintEnd_toEndOf="parent"
                 app:layout_constraintTop_toBottomOf="@+id/preview_card_container"
diff --git a/res/values/styles.xml b/res/values/styles.xml
index af7afb6..e18cff7 100644
--- a/res/values/styles.xml
+++ b/res/values/styles.xml
@@ -39,7 +39,6 @@
         <item name="android:fitsSystemWindows">false</item>
         <item name="android:windowDrawsSystemBarBackgrounds">true</item>
 
-        <item name="android:windowBackground">@android:color/transparent</item>
         <item name="android:windowContentOverlay">@null</item>
         <item name="android:windowDisablePreview">true</item>
     </style>