Fix confirm lock UI theme.

Now uses colorPrimary as its background color and sets colorAccent
directly. Some other mild cleanup as well.

BUG: 28760785

Change-Id: Ib8e5140b789449e518b498bc49438cb4a2bc6451
diff --git a/res/values/colors.xml b/res/values/colors.xml
index ab04c24..3b66469 100644
--- a/res/values/colors.xml
+++ b/res/values/colors.xml
@@ -78,7 +78,6 @@
     <color name="sim_noitification">@*android:color/material_deep_teal_500</color>
 
     <color name="warning">#ff5621</color>
-    <color name="confirm_device_credential_dark_background">#263238</color>
     <color name="confirm_device_credential_transparent_black">#60000000</color>
     <color name="fab_ripple">#1fffffff</color><!-- 12% white -->
     <color name="fab_shape">?android:attr/colorAccent</color>
diff --git a/res/values/themes.xml b/res/values/themes.xml
index 216b090..694c5c6 100644
--- a/res/values/themes.xml
+++ b/res/values/themes.xml
@@ -269,10 +269,10 @@
 
     <style name="Theme.ConfirmDeviceCredentialsDark" parent="@android:style/Theme.Material">
         <item name="android:colorPrimary">@color/primary_color</item>
-        <item name="android:colorPrimaryDark">@color/primary_dark_color</item>
+        <item name="android:colorAccent">@color/accent_color_lighter</item>
         <item name="android:windowActionBar">false</item>
         <item name="android:windowNoTitle">true</item>
-        <item name="android:windowBackground">@color/confirm_device_credential_dark_background</item>
+        <item name="android:windowBackground">?android:attr/colorPrimary</item>
 
         <item name="confirmDeviceCredentialsSideMargin">32dp</item>
         <item name="confirmDeviceCredentialsTopMargin">32dp</item>