Use card view for DSN

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

@@ -9,6 +9,9 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:orientation="vertical"
+        android:paddingHorizontal="6dp"
+        android:paddingVertical="12dp"
+        android:scrollbarStyle="outsideOverlay"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent">
 
@@ -16,6 +19,24 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content">
 
+            <androidx.cardview.widget.CardView
+                android:id="@+id/cardMessage"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_marginHorizontal="3dp"
+                app:cardBackgroundColor="?attr/colorCardBackground"
+                app:cardCornerRadius="6dp"
+                app:cardElevation="0dp"
+                app:layout_constraintEnd_toEndOf="parent"
+                app:layout_constraintStart_toStartOf="parent"
+                app:layout_constraintTop_toTopOf="parent">
+
+                <androidx.constraintlayout.widget.ConstraintLayout
+                    android:layout_width="match_parent"
+                    android:layout_height="wrap_content"
+                    android:paddingHorizontal="6dp"
+                    android:paddingVertical="12dp">
+
                     <eu.faircode.email.FixedTextView
                         android:id="@+id/tvHeaders"
                         android:layout_width="0dp"
@@ -36,6 +57,8 @@
                         android:layout_height="0dp"
                         app:constraint_referenced_ids="tvHeaders" />
                 </androidx.constraintlayout.widget.ConstraintLayout>
+            </androidx.cardview.widget.CardView>
+        </androidx.constraintlayout.widget.ConstraintLayout>
     </eu.faircode.email.ScrollViewEx>
 
     <eu.faircode.email.ContentLoadingProgressBar