Give your desktop a custom look
There are several ways to give your desktop—the background area of your screen—a custom look.
Change the picture you see on the desktop
In Desktop preferences, you can choose the picture that’s displayed on your desktop. Your Mac comes with dozens of desktop pictures to choose from, but you can also use your own pictures, or choose a solid color.
Tip: To quickly use a picture you have in the Photos app, select the picture in Photos, click the Share button 
in the Photos toolbar, then choose Set Desktop Picture.
Choose Apple menu > System Preferences, click Desktop & Screen Saver, then click Desktop.
On the left, find a picture or color:
Pictures and colors that come with your Mac: Click the disclosure triangle next to Apple, then select Desktop Pictures or Solid Colors.
Your pictures: Click the disclosure triangle next to Photos (or iPhoto if available). If your pictures are in the Pictures or another folder, click the triangle next to Folders, then select a folder.
To add a folder, click the Add button
, navigate to and select the folder, then click Choose.If you don’t see anything when you select the folder that contains your pictures, the pictures might not have the right file format— JPEG, PICT, TIFF, or PNG. To change a picture’s format, open it in the Preview app, then save it in the new format. If pictures look fuzzy, try using larger ones, such as 1024 x 768 pixels.
On the right, click the picture you want to use.
The desktop immediately changes, so you can see how the picture looks. When you use one of your own pictures, you can choose whether it should fill the screen, be centered, or be otherwise arranged. It’s easy to click around and try different pictures and arrangements until you find the one you like best.
If you can’t settle on just one picture, you can cycle through all the pictures in a folder. Select the “Change picture” checkbox, then choose how often you want the picture to change—for example, every hour. This option may affect the performance of some apps, such as games, that use many graphics. To use just one picture again, deselect the checkbox.
You can use a picture you see on the web as your desktop picture. Control-click the image, then select Use Image as Desktop Picture.
Use a screen saver
In Screen Saver preferences, you can choose a screen saver to hide the desktop when you’re away from your Mac.
Choose Apple menu > System Preferences, click Desktop & Screen Saver, then click Screen Saver.
Click a screen saver on the left, then set options for how it will look.
Source: Click the pop-up menu, then choose the pictures to show in the screen saver. You can use pictures that come with your Mac or choose pictures from your Photo Library or another folder.
The preview area shows how the screen saver will look; give it a moment to preview your selection.
Shuffle slide order: Select the checkbox to show pictures in a random order instead of their order in the source.
Set other options for the screen saver.
Start after: Click the pop-up menu, then select the amount of time you want your Mac to wait before starting the screen saver. For example, if you select 5 Minutes, the screen saver will start after your Mac is inactive for five minutes.
Show with clock: Select the checkbox to show the time in the screen saver.
Hot corners: Select the checkbox to set a shortcut for starting the screen saver.
To stop the screen saver and return to the desktop, press any key, move the mouse, or touch the trackpad.
If you want more security when you stop the screen saver, see Require a password after waking your Mac.
Make your menu bar and Dock dark
You can give your desktop a darker look by setting your menu bar and Dock to be dark.
Choose Apple menu > System Preferences, then click General.
Select “Use dark menu bar and Dock.”
Change button, menu, window, and highlight colors
Use the General pane of System Preferences to choose new colors for buttons, menus, windows, and selected text.
Choose Apple menu > System Preferences, then click General.
Click the Appearance pop-up menu, then choose a color to use for buttons, menus, and windows.
Click the “Highlight color” pop-up menu, then choose a color to use to highlight selected text.