<Style x:Key="RoundCornerTextStyle" TargetType="{x:Type TextBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Border x:Name="border" BorderBrush="{TemplateBinding BorderBrush}" CornerRadius="5" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" >
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>