如何获取 'hook_preprocess_block' 中的当前区域 ID?

How can I get the current region id inside the 'hook_preprocess_block'?

如何获取 hook_preprocess_block() 中的当前区域 ID?
我尝试了以下代码,但似乎有问题。

function ThemeName_preprocess_block(&$variables) {
  if ($variables['elements']['#region'] == "nav") {
    $variables['attributes']['class'][] = 'SomeStyle';
  }
}

$region = $variables['elements']['#configuration']['region'];