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How can I make all Resources in one place

I work on C# WPF
I have more than one DataGridView all of them has the same style (Background, row width, column height...etc) but each one has different numbers of columns
So my question is Can I make one style for these grids and share between them?
like css in Web

You can create a resource file in wpf where you can store all your style and template. Don't confuse it with the resource file in the Properties directory. You can add a Resource file by right clicking your project in visual studio and adding an existing xaml file or creating a new one.
After that, define all your styles and templates. Then you only need to include it in your available resources
<Application
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Class="UsingResourceDictionaries.App">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="myDirectory/myDictionary.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
Don't forget to give a key to each one of your style and template, so that you can use them in your User controls

The good practice for defining a reusable resources in WPF

I've been writing a CAD-style program in .Net, for this I have to have a lot of Brushes and Custom DashStyles.
So far I have defined them in a static class. for example:
public static readonly Brush GridBrushInModel = Brushes.DarkGray;
Now I can use the brush whenever I want. I have also Freezed them though.
My question is, is this the way this should be done? Or there are better ways? For example defining in ResourceDictionary? How it is done?

Shared resources in a WPF application are typically stored as a ResourceDictionary. Each dictionary should have its own XAML file (if you wish to split up your resources).
They are pretty easy to define:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="MyCoolBrush" Color="Black"/>
</ResourceDictionary>
Note that I gave the element a x:Key attribute. This is what you use to reference the resource later.
Finally, you have to merge the dictionary into the using code. This can be done at any level, though its most commonly done in the Window.Resources or in App.xaml.
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Resources/MyBrushes.xaml"/>
</ResourceDictionary.MergedDictionaries>
...
</ResourceDictionary>
</Window.Resources>
Once you have them, you can reference them in XAML like this:
<Grid Background={StaticResource MyCoolBrush}/>

WPF's application wide styles in Windows Forms context

We migrate from WinForms to WPF... slowly =)
No we use WPF User Controls with ElementHost.
Is it possible to define application wide resources in this context? In pure WPF Application.Resources stands for it. But there's no WPF App when integrating with WinForms.

You can use a WPF application object even if your project is a WinForms one with a few separate WPF forms or controls. The object won't be precreated for you, but if you manually create it, simply by new App() (or even without a derived class, new System.Windows.Application()), everything in your project will see it.

You can create a common ResourceDictionary and add it to the Resources of your UserControls. That way you just have to change your Styles in one location.
Dictionary1.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
</ResourceDictionary>
and add it to your UserControl using MergedDictionarys
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Dictionary1.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
or just add it to the Control's Resources like this
<UserControl.Resources>
<ResourceDictionary Source="Dictionary1.xaml"/>
</UserControl.Resources>

How to import one ResourceDictionary into other, in WPF?

Is it possible to add one resource dictionary into other one?

In Dictionary2.xaml define MergedDictionaries (right after the opening ResourceDictionary tag):
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Path/to/Dictionary1.xaml" />
</ResourceDictionary.MergedDictionaries>
there's a catch: each time you merge dictionaries you effectively create a copy of the merged dictionary. And it's recursive - if you have Dict3.xaml and Dict4.xaml that both load Dictionary2.xaml, you will have three instances of Dictionary1.xaml created
The solution is a SharedResourceDictionary. The implementation in the tutorial should be seen as a starting point and will probably need some level of tweaking - depending on use scenario. Google "wpf SharedResourceDictionary" for some gotchas and solutions.
From answer to this question by XAMeLi

A snippet straight from a sketchflow project I am working on that shows how to merge resource dictionaries in xaml:
<Application.Resources>
<!-- Resources scoped at the Application level should be defined here. -->
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Microsoft.Expression.Prototyping.SketchControls;component/ScrollViewerStyles.xaml"/>
<ResourceDictionary Source="/[ProjectABC];component/[fileXYZ].xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
This shows merging two additional resource dictionaries into another resource dictionary.
(Note that the order can become important if you have default styles defined in more than one place as they will override each other)

Something like:
ResourceDictionary resources = new ResourceDictionary();
resources.Source = new Uri("/MyModule;component/MyModule.xaml",
UriKind.RelativeOrAbsolute);
Application.Current.Resources.MergedDictionaries.Add(resources);
Might be what you're looking for. We use code like this in our Prism Modules.

Xaml: C# How to keep style consistent

I'm working on a semi-large windows application using wpf and C# in VS 2010. While working on the xaml, I added a tag so that all buttons and datagrids are styled in the same way. I've copied and pasted this block into several of my .xaml files and that works fine. Of course the problem I'm running into now is that I've added to and changed the style several times.
What is the best way to keep style consistent between my different Windows? Is it subclassing, using Resources.resx, or another way enirely?

If you define the style in the Application level ResourceDictionary (App.xaml), then it will automatically be inherited by your other XAML Windows/Controls.

yeah, if you were to create a new file called Resources.xaml and then add this to your Application.xaml file:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Resources.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
then you should be able to reference the styles in the Resources.xaml from all the windows in your application.