def METHOD_NAME(themes_base_dir=None):
    """
    Get all the theme dirs directly under a given base dir.
    Args:
        themes_base_dir (Path): base dir that contains themes.
    Returns:
        List of theme dir names (relative to the base dir) or empty list if the base themes dir does not exist or there
        are no containing theme dirs.
    """
    try:
        themes_base_dir_listing = os.listdir(themes_base_dir)
    except FileNotFoundError:
        themes_base_dir_listing = []
    return [_dir for _dir in themes_base_dir_listing if is_theme_dir(themes_base_dir / _dir)]