Auto-hide the launcher
You can hide the launcher if you only want to see it when you move your mouse or touchpad pointer to the left side of the screen.
點擊選單列最右邊的圖示，選擇系統設定值。
In the Personal section, click Appearance.
Switch to the Behavior tab.
Switch Auto-hide the Launcher on.
To help prevent you from accidentally showing the launcher, Ubuntu requires you to push a little bit harder with your mouse or touchpad pointer to make the launcher show. You can adjust the force needed by setting the Reveal sensitivity lower or higher.