detect/detect.gui/Assets/CalendarDatePicker.axaml

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

  <Style Selector="CalendarDatePicker">
    <Setter Property="Foreground" Value="{DynamicResource CalendarDatePickerForeground}" />
    <Setter Property="BorderThickness" Value="{DynamicResource CalendarDatePickerBorderThemeThickness}" />
    <Setter Property="CornerRadius" Value="6" />
    <Setter Property="HorizontalAlignment" Value="Left" />
    <Setter Property="VerticalAlignment" Value="Center" />
    <Setter Property="HorizontalContentAlignment" Value="Center" />
    <Setter Property="VerticalContentAlignment" Value="Center" />
    <Setter Property="Padding" Value="4" />
    <Setter Property="Template">
      <ControlTemplate>
        <DataValidationErrors>
          <Panel x:Name="LayoutRoot"
                 HorizontalAlignment="Stretch"
                 VerticalAlignment="Stretch">
            <Border x:Name="Background"
                    CornerRadius="{TemplateBinding CornerRadius}"
                    BorderThickness="{TemplateBinding BorderThickness}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    Background="{TemplateBinding Background}" />
            <Grid ColumnDefinitions="*,Auto">
              <TextBox Name="PART_TextBox"
                       Foreground="{TemplateBinding Foreground}"
                       Background="Transparent"
                       BorderBrush="Transparent"
                       BorderThickness="0"
                       CornerRadius="{TemplateBinding CornerRadius}"
                       Margin="4, 1, 1, 1"
                       Padding="{TemplateBinding Padding}"
                       Watermark="{TemplateBinding Watermark}"
                       UseFloatingWatermark="{TemplateBinding UseFloatingWatermark}"
                       HorizontalAlignment="Stretch"
                       VerticalAlignment="Stretch"
                       Focusable="False"
                       VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                       HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                       Grid.Column="0">
                <TextBox.Styles>
                  <Style Selector="TextBox#PART_TextBox:pointerover">
                    <Setter Property="BorderThickness" Value="0" />
                  </Style>
                  <Style Selector="TextBox#PART_TextBox:focus">
                    <Setter Property="BorderThickness" Value="1" />
                  </Style>
                  <Style Selector="TextBox#PART_TextBox:focus /template/ Border#PART_BorderElement">
                    <Setter Property="Background" Value="Transparent"/>
                    <Setter Property="BorderBrush" Value="Transparent"/>
                    <Setter Property="BorderThickness" Value="0" />
                  </Style>
                  <Style Selector="TextBox#PART_TextBox:disabled">
                    <Style Selector="^ /template/ Border#PART_BorderElement">
                      <Setter Property="Background" Value="Transparent" />
                      <Setter Property="BorderBrush" Value="Transparent" />
                    </Style>
                    <Style Selector="^ /template/ TextBlock#PART_Watermark, ^ TextBlock#PART_FloatingWatermark">
                      <Setter Property="TextElement.Foreground" Value="{DynamicResource CalendarDatePickerTextForegroundDisabled}" />
                    </Style>
                  </Style>
                </TextBox.Styles>
              </TextBox>
              <Button Name="PART_Button"
                      Margin="2,0,4,0"
                      Width="24"
                      Height="20"
                      Grid.Column="1"
                      Focusable="False">
                <Button.Template>
                  <ControlTemplate>
                    <PathIcon Width="12" 
                              Height="12"
                              Foreground="#FFFFFF"
                              Data="M1939 486L2029 576L1024 1581L19 576L109 486L1024 1401L1939 486Z" />
                  </ControlTemplate>
                </Button.Template>
              </Button>
              <Popup Grid.Column="0"
                     Name="PART_Popup"
                     PlacementTarget="{TemplateBinding}"
                     IsLightDismissEnabled="True">
                <Calendar Name="PART_Calendar"
                          CornerRadius="6, 6, 0, 0"
                          Margin="0, 5, 0, 0"
                          FirstDayOfWeek="{TemplateBinding FirstDayOfWeek}"
                          IsTodayHighlighted="{TemplateBinding IsTodayHighlighted}"
                          SelectedDate="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=SelectedDate, Mode=TwoWay}"
                          DisplayDate="{TemplateBinding DisplayDate}"
                          DisplayDateStart="{TemplateBinding DisplayDateStart}"
                          DisplayDateEnd="{TemplateBinding DisplayDateEnd}" />
              </Popup>
            </Grid>
          </Panel>
        </DataValidationErrors>
      </ControlTemplate>
    </Setter>
  </Style>
  
  <Style Selector="CalendarDatePicker.filter">
    <Setter Property="FontFamily" Value="{StaticResource Font-Family}" />
    <Setter Property="FontSize" Value="14" />
    <Setter Property="Background">
      <Setter.Value>
        <SolidColorBrush Color="#2D77F3" Opacity="0.2" />
      </Setter.Value>
    </Setter>    
    <Setter Property="BorderBrush">
      <Setter.Value>
        <SolidColorBrush Color="#2D77F3" Opacity="0.3" />
      </Setter.Value>
    </Setter>    
    <Setter Property="CornerRadius" Value="6" />
    
    <!-- Pointer-over State -->
    <Style Selector="^:pointerover /template/ Border#Background">
      <Setter Property="Background">
        <Setter.Value>
          <SolidColorBrush Color="#2D77F3" Opacity="0.3" />
        </Setter.Value>
      </Setter>    
      <Setter Property="BorderBrush">
        <Setter.Value>
          <SolidColorBrush Color="#2D77F3" Opacity="0.4" />
        </Setter.Value>
      </Setter>   
    </Style>

    <!-- Focused State -->
    <Style Selector="^:focus-within:not(CalendarDatePicker:focus) /template/ Border#Background">
      <Setter Property="Background">
        <Setter.Value>
          <SolidColorBrush Color="#2D77F3" Opacity="0.3" />
        </Setter.Value>
      </Setter>    
      <Setter Property="BorderBrush">
        <Setter.Value>
          <SolidColorBrush Color="#2D77F3" Opacity="0.4" />
        </Setter.Value>
      </Setter>   
      <Setter Property="BorderThickness" Value="1" />
    </Style>
  </Style>
</Styles>