Rsource style.css not Found

Hi,
i'm new in xamarin Forms and i'm developing my first App. I have an issue tryng to use Css StyleSheet. i have done a lot of test but i recive always the same error : Reosurce not found. My file style.css' actions is on EmbeddedSource. I tried to put it in share project root or in Asset of Android project but always the same error. This is my code:

<ContentPage.Resources>
    <StyleSheet Source="/styles.css" />
    <ResourceDictionary>
        <vm:LoginViewModel x:Key="viewmodel" />
    </ResourceDictionary>
</ContentPage.Resources>

I read every forum or solution for this problem but nothing solved my issue.I have last version of xamarin on VS2017 Community

Waiting your answer ASAP,
Alessandro