To change your theme from Day Mode to Night Mode or Midnight Mode in Final Draft Cloud, click your profile icon in the top right.
In the new menu that opens, select the theme you would like from Day, Night or Midnight Mode, and you'll see the screen shift to reflect your preference.
Please note that your theme will not change the color of your text or page when saving your document as a PDF or printing from Final Draft Cloud, it will always be black text on a white background.