Customize toolbars
Many windows contain a toolbar with buttons that provide quick access to frequently used features, tools, or actions. You can hide the toolbar, or choose which buttons to include and how they appear.
Hide or show the toolbar: Choose View > Hide Toolbar or View > Show Toolbar. While working in full screen for some apps, choose View > Always Show Toolbar in Full Screen.
Remove a button: Hold down the Command key while you drag the item out of the toolbar until you see or hear a “poof” effect.
Rearrange buttons: Hold down the Command key while you drag an item around in the toolbar, then drop the item when an open space appears.
Add a button: Choose View > Customize Toolbar, then drag an item from the palette to the toolbar until you see a green plus sign.
Change how buttons appear: For some toolbars, you can show labels with the buttons. Choose View > Customize Toolbar, click the Show pop-up menu, then choose an option.
When you resize a window, toolbar buttons can become hidden as the window narrows. To see a list of the hidden items, click the double arrows 
at the end of the toolbar.
If your Mac has a Touch Bar, many apps—like Mail or Safari—let you customize it.