EDIT

Author: pieckenst

src/PleasantUI/Styling/ControlThemes/PleasantControls/ItemListPanel.axaml

@@ -19,6 +19,7 @@
         <Setter Property="CornerRadius"    Value="{DynamicResource ControlCornerRadius}" />
         <Setter Property="HorizontalAlignment" Value="Stretch" />
         <Setter Property="VerticalAlignment"   Value="Stretch" />
+        <Setter Property="SearchBoxCornerRadius" Value="{DynamicResource ControlCornerRadius}" />
 
         <Setter Property="Template">
             <ControlTemplate>
@@ -39,7 +40,7 @@
                                     Background="{DynamicResource BackgroundColor1}"
                                     BorderBrush="{DynamicResource ControlBorderColor}"
                                     BorderThickness="{DynamicResource ControlBorderThickness}"
-                                    CornerRadius="{DynamicResource ControlCornerRadius}"
+                                    CornerRadius="{TemplateBinding SearchBoxCornerRadius}"
                                     Padding="0">
                                 <Grid ColumnDefinitions="Auto,*,Auto">
                                     <PathIcon Grid.Column="0"

src/PleasantUI/Styling/ControlThemes/PleasantControls/TreeViewPanel.axaml

@@ -140,6 +140,7 @@
         <Setter Property="CornerRadius"    Value="{DynamicResource ControlCornerRadius}" />
         <Setter Property="HorizontalAlignment" Value="Stretch" />
         <Setter Property="VerticalAlignment"   Value="Stretch" />
+        <Setter Property="SearchBoxCornerRadius" Value="{DynamicResource ControlCornerRadius}" />
 
         <Setter Property="Template">
             <ControlTemplate>
@@ -174,7 +175,7 @@
                                         Background="{DynamicResource BackgroundColor1}"
                                         BorderBrush="{DynamicResource ControlBorderColor}"
                                         BorderThickness="{DynamicResource ControlBorderThickness}"
-                                        CornerRadius="{DynamicResource ControlCornerRadius}"
+                                        CornerRadius="{TemplateBinding SearchBoxCornerRadius}"
                                         Padding="0"
                                         HorizontalAlignment="Stretch">
                                     <Grid ColumnDefinitions="Auto,*,Auto">

src/PleasantUI/Styling/VGUIControlStyles.axaml

@@ -136,13 +136,13 @@
     </Style>
 
     <!-- VGUI TreeViewPanel search box — square corners -->
-    <Style Selector="controls|TreeViewPanel /template/ Border#PART_SearchBoxBorder">
-        <Setter Property="CornerRadius" Value="0" />
+    <Style Selector="controls|TreeViewPanel">
+        <Setter Property="SearchBoxCornerRadius" Value="0" />
     </Style>
 
     <!-- VGUI ItemListPanel search box — square corners -->
-    <Style Selector="controls|ItemListPanel /template/ Border#PART_SearchBoxBorder">
-        <Setter Property="CornerRadius" Value="0" />
+    <Style Selector="controls|ItemListPanel">
+        <Setter Property="SearchBoxCornerRadius" Value="0" />
     </Style>
 
     <!-- VGUI ShadowBorder — square corners (used by ContentDialog shadow) -->