Default the TextBoxBase/PasswordBox SelectionBrush to PrimaryHueLightBrush as per the material spec https://material.io/design/color/text-legibility.html#text-types (#2469)

Author: JeffBarnard

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PasswordBox.xaml

@@ -20,6 +20,7 @@
         <Setter Property="wpf:TextFieldAssist.TextBoxViewMargin" Value="{x:Static wpf:Constants.DefaultTextBoxViewMargin}" />
         <Setter Property="Background" Value="Transparent"/>
         <Setter Property="CaretBrush" Value="{DynamicResource PrimaryHueMidBrush}" />
+        <Setter Property="SelectionBrush" Value="{DynamicResource PrimaryHueLightBrush}" />
         <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
         <Setter Property="VerticalContentAlignment" Value="Top"/>
         <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
@@ -392,16 +393,7 @@
                     </ControlTemplate.Triggers>
                 </ControlTemplate>
             </Setter.Value>
-        </Setter>
-        <Style.Triggers>
-            <MultiTrigger>
-                <MultiTrigger.Conditions>
-                    <Condition Property="IsInactiveSelectionHighlightEnabled" Value="true"/>
-                    <Condition Property="IsSelectionActive" Value="false"/>
-                </MultiTrigger.Conditions>
-                <Setter Property="SelectionBrush" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
-            </MultiTrigger>
-        </Style.Triggers>
+        </Setter>        
     </Style>
 
     <Style x:Key="MaterialDesignFloatingHintPasswordBox" TargetType="{x:Type PasswordBox}" BasedOn="{StaticResource MaterialDesignPasswordBox}">

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.TextBox.xaml

@@ -43,6 +43,7 @@
         <Setter Property="wpf:TextFieldAssist.TextBoxViewMargin" Value="{x:Static wpf:Constants.DefaultTextBoxViewMargin}" />
         <Setter Property="Background" Value="Transparent"/>
         <Setter Property="CaretBrush" Value="{DynamicResource PrimaryHueMidBrush}" />
+        <Setter Property="SelectionBrush" Value="{DynamicResource PrimaryHueLightBrush}" />
         <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
         <Setter Property="VerticalContentAlignment" Value="Top"/>
         <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
@@ -481,16 +482,7 @@
                     </ControlTemplate.Triggers>
                 </ControlTemplate>
             </Setter.Value>
-        </Setter>
-        <Style.Triggers>
-            <MultiTrigger>
-                <MultiTrigger.Conditions>
-                    <Condition Property="IsInactiveSelectionHighlightEnabled" Value="true"/>
-                    <Condition Property="IsSelectionActive" Value="false"/>
-                </MultiTrigger.Conditions>
-                <Setter Property="SelectionBrush" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
-            </MultiTrigger>
-        </Style.Triggers>
+        </Setter>        
     </Style>
 
     <Style x:Key="MaterialDesignTextBox" TargetType="{x:Type TextBox}" BasedOn="{StaticResource MaterialDesignTextBoxBase}" />