Getting error in new CSS Styles in Xamarin.Forms

I created new project and add CSS folder to the solution explorer and add Stylesheet1.css add to the folder after that jest add the ContentPage baground color in Stylesheet1.css and acessing in XAML page and run the project i am getting error is,

 

 

Any one help me how to solve this error every time getting same error  

 

Thanks,

sudheer