Admin can select one of the preferred themes between the couple of theme choices available. Available admin side themes have different positioning of main navigation, colors and arrangement of the dashboard widgets. Here is how you select and customize the theme of your choice..
Navigate to Admin Themes
Admin Main Navigation->Setup–>Themes->Admin Themes
Just like the way we activate theme for the client side, drag the cursor to the theme of your choice, click “Active Theme” when it appears on your screen, and the newly selected theme will be activated for the admin to login and use. Further customization of the activated theme is also possible by clicking “Theme Settings”.
Theme settings will appear only for the currently activated theme, and it appears underneath “Active Theme” while you hover on the active theme. Settings will not appear for the inactive theme. On the settings page, you can customize the theme with your desired color combination without the need to write extra CSS. You can use color picker to make right color combination of theme elements and fonts.
Click “Save Theme Settings” to save your color preference, or click “Reset” return to the former color settings.
Image#MS-5.13.1: Activating the Theme and Customizing Theme Settings