Set a padding on dataGridCells in WPF

The problem is that the Padding isn’t transfered to the Border that’s in the Template for DataGridCell. You can edit the Template and add the TemplateBinding for Padding

<DataGrid ...>
    <DataGrid.CellStyle>
        <Style TargetType="DataGridCell">
            <Setter Property="Padding" Value="20"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type DataGridCell}">
                        <Border Padding="{TemplateBinding Padding}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
                            <ContentPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DataGrid.CellStyle>
    <!--...-->
</DataGrid>