May i know how to set the window style or color? The image below is my WPF

I want to set my window become something like the app below:

Thanks.
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As far as I can remember (It is more than 4 years ago), you can create a style to use with a WPF window.
This is a sample window Style:
And the result will look like this:
Read more on Create Custom Windows in WPF with Ease