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This plugin adds Theme menus in the admin bar. 
You can switch and activate the theme on the admin bar. 
You don’t need to go to the administration screens to switch the theme.
(For Japanese User) 管理バーにテーマメニューを追加します。 管理バー上でサイトテーマの変更・有効化が行えます。 テーマを変更するために管理画面に行く? 要がなくなります。

Switch theme on admin bar

This plugin adds Theme menus in the admin bar. You can switch and activate the theme on the admin bar.

Marcel Bootsman

Auto Hide Admin Bar makes the WordPress Toolbar disappear – and reappear when hovering the mouse pointer over the top of the browser window. 
You end up with a clean view of your site, and keep having access to the WordPress Toolbar. 
If you have any comments or questions, please use the <a href="https://wordpress.org/support/plugin/auto-hide-admin-bar" rel="ugc">support forum</a>.

Auto Hide Admin Bar

This plugin adds an auto-hide feature to the WordPress Admin Bar or Toolbar.

Switch theme on admin bar vs Auto Hide Admin Bar