Where can I enter my custom CSS Code?

Step 1: Go to Appearance > Customize > Custom Code > Custom CSS

Step 2: Use the Custom CSS field to insert your custom CSS code. You can use the Medium Devices CSS field to insert additional code only for medium size screens and the Small Devices CSS field to insert additional code only for small screen devices.

You can use the Header Code field to insert additional code before </head> tag and the Footer Code field to insert additional code before </footer> tag.