private void ThemePicker_SelectedIndexChanged(object sender, EventArgs e)
{
var theme = themePicker.Items[themePicker.SelectedIndex];
var app = (Application.Current as App);
app.Properties[Themes.ThemeKey] = theme;
app.SavePropertiesAsync();
var themeLoader = new ThemeLoader();
themeLoader.LoadTheme();
themeLoader.SetNavigationBarColor();
ExitPage();
}