修复button文字显示不全的问题

src/Downkyi/Themes/Default/Styles/Button.axaml

@@ -5,6 +5,7 @@
         <Setter Property="Height" Value="30" />
         <Setter Property="Width" Value="80" />
         <Setter Property="CornerRadius" Value="5" />
+        <Setter Property="Padding" Value="0" />
         <Setter Property="HorizontalContentAlignment" Value="Center" />
         <Setter Property="VerticalContentAlignment" Value="Center" />
         <Setter Property="TextBlock.Foreground" Value="White" />