Ported changes from #1543.

Fix a few theming issues.

Author: grokys

src/GitHub.VisualStudio.UI/Styles/ThemeBlue.xaml

@@ -64,5 +64,6 @@
 
   <SolidColorBrush x:Key="GitHubPeekViewBackground" Color="#F5F5F5" />
   <SolidColorBrush x:Key="GitHubPendingReviewBackground" Color="#FFF8C7" />
-  <SolidColorBrush x:Key="GitHubMultilineListItemActiveBrush" Color="#FFCCCEDB"/>
+  <SolidColorBrush x:Key="GitHubMultilineListItemActiveBrush" Color="#FFCCCEDB" />
+  <SolidColorBrush x:Key="GitHubFileExpanderHeaderBackgroundBrush" Color="#FFD6DBE9" />
 </ResourceDictionary>

src/GitHub.VisualStudio.UI/Styles/ThemeDark.xaml

@@ -65,4 +65,5 @@
   <SolidColorBrush x:Key="GitHubPeekViewBackground" Color="#252526" />
   <SolidColorBrush x:Key="GitHubPendingReviewBackground" Color="#26384D" />
   <SolidColorBrush x:Key="GitHubMultilineListItemActiveBrush" Color="#FF3F3F46"/>
+  <SolidColorBrush x:Key="GitHubFileExpanderHeaderBackgroundBrush" Color="#FF2D2D30" />
 </ResourceDictionary>

src/GitHub.VisualStudio.UI/Styles/ThemeLight.xaml

@@ -65,4 +65,5 @@
   <SolidColorBrush x:Key="GitHubPeekViewBackground" Color="#F5F5F5" />
   <SolidColorBrush x:Key="GitHubPendingReviewBackground" Color="#FFF8C7" />
   <SolidColorBrush x:Key="GitHubMultilineListItemActiveBrush" Color="#FFCCCEDB"/>
+  <SolidColorBrush x:Key="GitHubFileExpanderHeaderBackgroundBrush" Color="#FFEEEEF2" />
 </ResourceDictionary>

src/GitHub.VisualStudio/Views/GitHubPane/PullRequestFileCommentsView.xaml

@@ -42,8 +42,8 @@
                         <Setter Property="Template">
                             <Setter.Value>
                                 <ControlTemplate TargetType="{x:Type GroupItem}">
-                                    <Expander Background="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"
-                                              Foreground="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"
+                                    <Expander Background="{DynamicResource GitHubFileExpanderHeaderBackgroundBrush}"
+                                              Foreground="{DynamicResource VsBrush.WindowText}"
                                               IsExpanded="True"
                                               Padding="0 4 4 4">
                                         <Expander.Header>
@@ -53,6 +53,7 @@
                                                 <ghfvs:OcticonImage DockPanel.Dock="Right" Icon="comment" Margin="2 0 2 -2"/>
                                                 <ghfvs:TrimmedPathTextBlock Grid.Column="1"
                                                                             FontWeight="SemiBold"
+                                                                            Foreground="{DynamicResource VsBrush.WindowText}"
                                                                             Text="{Binding Name}"
                                                                             ToolTip="{Binding Name}"/>
                                             </DockPanel>
@@ -61,7 +62,7 @@
                                                       Grid.IsSharedSizeScope="True">
                                             <ItemsControl.ItemTemplate>
                                                 <DataTemplate>
-                                                    <Border BorderBrush="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"
+                                                    <Border BorderBrush="{DynamicResource GitHubFileExpanderHeaderBackgroundBrush}"
                                                             BorderThickness="1 0 1 1">
                                                         <ghfvs:GitHubActionLink Command="{Binding Open}"
                                                                                 Content="{Binding Body, Converter={ghfvs:TrimNewlinesConverter}, Mode=OneWay}"

src/GitHub.VisualStudio/Views/GitHubPane/PullRequestUserReviewsView.xaml

@@ -69,7 +69,7 @@
                                         </TextBlock>
                                     </StackPanel>
                                 </Expander.Header>
-                                <StackPanel Margin="16 4 0 4"
+                                <StackPanel Margin="21 4 0 4"
                                             Visibility="{Binding HasDetails, Converter={ghfvs:BooleanToVisibilityConverter}}">
                                     <Expander Foreground="{DynamicResource GitHubVsToolWindowText}"
                                               IsExpanded="True"