Better layout padding for main view

app/src/main/res/layout-land/fragment_main.xml

@@ -3,7 +3,11 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="horizontal"
-    android:baselineAligned="false" >
+    android:baselineAligned="false"
+    android:paddingLeft="@dimen/activity_horizontal_margin"
+    android:paddingRight="@dimen/activity_horizontal_margin"
+    android:paddingTop="@dimen/activity_vertical_margin"
+    android:paddingBottom="@dimen/activity_vertical_margin" >
 
     <LinearLayout
         android:layout_width="0dp"

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

@@ -2,7 +2,11 @@
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:orientation="vertical" >
+    android:orientation="vertical"
+    android:paddingLeft="@dimen/activity_horizontal_margin"
+    android:paddingRight="@dimen/activity_horizontal_margin"
+    android:paddingTop="@dimen/activity_vertical_margin"
+    android:paddingBottom="@dimen/activity_vertical_margin" >
 
     <ImageView
         android:id="@+id/main_lights"

app/src/main/res/values-sw720dp-land/dimens.xml

+<resources>
+    <!--
+         Customize dimensions originally defined in res/values/dimens.xml (such as
+         screen margins) for sw720dp devices (e.g. 10" tablets) in landscape here.
+    -->
+    <dimen name="activity_horizontal_margin">128dp</dimen>
+</resources>

app/src/main/res/values-w820dp/dimens.xml

+<resources>
+    <!-- Example customization of dimensions originally defined in res/values/dimens.xml
+         (such as screen margins) for screens with more than 820dp of available width. This
+         would include 7" and 10" devices in landscape (~960dp and ~1280dp respectively). -->
+    <dimen name="activity_horizontal_margin">64dp</dimen>
+</resources>

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

 <resources>
+    <!-- Default screen margins, per the Android Design guidelines. -->
+    <dimen name="activity_horizontal_margin">16dp</dimen>
+    <dimen name="activity_vertical_margin">16dp</dimen>
+
     <dimen name="step_pager_tab_width">32dp</dimen>
     <dimen name="step_pager_tab_height">3dp</dimen>
     <dimen name="step_pager_tab_spacing">4dp</dimen>