Set RegionColor
MODIFY
WalletWasabi.Fluent/Styles/Themes/BaseDark.xaml
WalletWasabi.Fluent/Styles/Themes/BaseDark.xaml
<SolidColorBrush x:Key="TextControlForeground">#ACACAC</SolidColorBrush>
<SolidColorBrush x:Key="TextControlBorderBrush">#0078D4</SolidColorBrush>
<SolidColorBrush x:Key="TextControlBorderBrushFocused">#47AFFF</SolidColorBrush>
+ <Color x:Key="RegionColor">#FF212121</Color>
</Styles.Resources>
<StyleInclude Source="avares://Avalonia.Themes.Fluent/Accents/FluentDark.xaml"/>
</Styles>

MODIFY
WalletWasabi.Fluent/Styles/Themes/BaseLight.xaml
WalletWasabi.Fluent/Styles/Themes/BaseLight.xaml
<SolidColorBrush x:Key="TextControlForeground">#737373</SolidColorBrush>
<SolidColorBrush x:Key="TextControlBorderBrush">#0B7ED5</SolidColorBrush>
<SolidColorBrush x:Key="TextControlBorderBrushFocused">#2A9CF4</SolidColorBrush>
+ <Color x:Key="RegionColor">#FF212121</Color>
</Styles.Resources>
<StyleInclude Source="avares://Avalonia.Themes.Fluent/Accents/FluentLight.xaml"/>
</Styles>

MODIFY
WalletWasabi.Fluent/Views/MainView.axaml
WalletWasabi.Fluent/Views/MainView.axaml
</Panel>
</SplitView.Pane>
<Panel>
- <Border Background="#212121" BoxShadow="0 1 4 #131313" IsHitTestVisible="False" />
+ <Border Background="{DynamicResource RegionColor}" BoxShadow="0 1 4 #131313" IsHitTestVisible="False" />
<DockPanel>
<local:StatusBar DockPanel.Dock="Bottom" DataContext="{Binding StatusBar}" VerticalAlignment="Bottom" Height="32" TextBlock.FontSize="12" />
<Panel Margin="20 10 20 0">

Set RegionColor