Custom Codes
Header Code
Go to Appearance > Customize > Custom Codes section. Add your before </head> code under Header Code. e.g. Google Analytics and click Save button.
Footer Code
Go to Appearance > Customize > Custom Codes section. Add your before </body> code under Footer code and Save.
Custom CSS
Go to Appearance > Customize > Custom Codes section. Enter your CSS code under Custom CSS and Save.