private void UpdateThemesList() {
var dir = FilesStorage.Instance.GetDirectory("Themes");
var files = FileUtils.GetFilesSafe(dir, "*.xaml");
Themes.ReplaceEverythingBy(files.Any()
? BuiltInThemes.OfType<object>().Append(new Separator()).Concat(files.Select(x => new ThemeLink(x)))
: BuiltInThemes);
SelectedTheme?.Update();
}