bitwarden-mobile/src/App/App.xaml.cs

using Bit.App.Pages;
using System;
using System.Reflection;
using Xamarin.Forms;
using Xamarin.Forms.StyleSheets;
using Xamarin.Forms.Xaml;

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace Bit.App
{
    public partial class App : Application
    {
        public App()
        {
            InitializeComponent();

            // TODO: Load theme?
            if(false)
            {
#pragma warning disable CS0162 // Unreachable code detected
                Resources.Add(
#pragma warning restore CS0162 // Unreachable code detected
                    StyleSheet.FromAssemblyResource(IntrospectionExtensions.GetTypeInfo(typeof(App)).Assembly,
                    "Bit.App.Css.dark.css"));
            }
            Resources.Add(
                StyleSheet.FromAssemblyResource(IntrospectionExtensions.GetTypeInfo(typeof(App)).Assembly,
                "Bit.App.Css.styles.css"));
            Resources.Add(
                StyleSheet.FromAssemblyResource(IntrospectionExtensions.GetTypeInfo(typeof(App)).Assembly,
                $"Bit.App.Css.{Device.RuntimePlatform.ToLowerInvariant()}.css"));

            MainPage = new TabsPage();
        }

        protected override void OnStart()
        {
            // Handle when your app starts
        }

        protected override void OnSleep()
        {
            // Handle when your app sleeps
        }

        protected override void OnResume()
        {
            // Handle when your app resumes
        }
    }
}