It makes absolutely no sense to put any style
inside of the XAML element. If you could, how could you possibly reuse it? If you don't need a style reuse, why having it at all?
If you need to do it for only one element, you can directly add all those properties to it:
<DataGrid FontSize="...", FondFamily="..." FontWeigh="..." ... >
</DataGrid>
If you need to be consistent with other elements, possibly of different type, for consistency, you can create a resource dictionary and reference all the property from this dictionary one by one. Using Resource Dictionaries is explained here:
http://msdn.microsoft.com/en-us/library/cc903952%28v=vs.95%29.aspx[
^].
You can use the defined resource element using the
StaticResource
binding:
http://msdn.microsoft.com/en-us/library/cc903952%28v=vs.95%29.aspx#referencing_resources_from_xaml[
^].
You can define a resource dictionary separate from your window-type XAML using the
merged resource dictionaries; this way, you can reuse the original external resource dictionary (referenced by its relative file name) in more than one window or user control type:
http://msdn.microsoft.com/en-us/library/aa350178%28v=vs.110%29.aspx[
^].
Finally, you can use styles are reuse them for different elements and different windows or user controls:
http://msdn.microsoft.com/en-us/library/ms745683%28v=vs.110%29.aspx[
^],
http://wpftutorial.net/Styles.html[
^].
—SA