Mastodon/app/javascript/mastodon/features/notifications_v2/components/notification_collection.module.scss

.actions {
  display: flex;
  align-items: center;
}

.menuButton {
  box-sizing: content-box;
  margin-inline-start: auto;
  padding: 4px;
  border-radius: 4px;
  border: 1px solid var(--color-border-primary);

  svg {
    width: 20px;
    height: 20px;
  }
}