Working in dark mode in Write by Zaweba
Write by Zaweba has a light and a dark interface. In dark mode the window darkens but the page stays white, so you still see the real document.

Some people write late at night, and a bright white window can be tiring then. Others work in a dim room, or simply prefer darker screens. Write by Zaweba has a light and a dark interface, so the window can suit you and the room you are in.
What changes and what doesn't
In dark mode, the menus, toolbars, panes and the area around the pages turn dark. The page itself stays white paper. That is a deliberate choice. Write draws pages as they will print, and a white page with dark text is what you will get on paper and in a PDF. Keeping it white means the colours you choose for text, highlights and shading are shown truthfully.
Many dark modes in other programs invert the page, so black text turns white on a dark background. That can be easier on the eyes, but it hides how the document really looks. A pale yellow highlight can vanish, and a dark blue heading can look odd. In Write, what you see on the page is what you will print, in either theme.
Choosing a theme
Light mode suits bright rooms and daytime work. The whole window is pale, matching the page, and the contrast between the interface and the paper is low.
Dark mode suits dim rooms and evening work. The interface fades back, so the white page stands out. Some people find that this focus helps them concentrate on the text, since the toolbar and menus draw less attention.
Neither is right or wrong. Try both for a day or two and keep the one you prefer.
Comfort for long sessions
Theme is only part of comfort. Zoom helps too: page width makes text larger on wide screens, and zooming in is better than increasing font sizes, because the document stays correctly sized for printing.
Focus mode, turned on with F11, goes further. It shows just the pages full screen with typewriter scrolling, which keeps the line you are typing in a steady place on the screen. Combined with dark mode, it gives a calm, uncluttered space to write in the evening.
Breaks matter as well. No theme makes hours of staring at a screen good for your eyes. Look away now and then, and blink.
Checking colours in either theme
Because the page stays white, colour choices are safe to judge in either theme. If a highlight or a shaded paragraph looks too faint, it will look too faint on paper as well, so fix it there and then. Pale text colours that seem fine against a dark interface can still be hard to read on a white page, which is exactly what the page shows you. For documents that will be printed in black and white, print preview is still the final check.
Your files are unaffected
The theme belongs to the shared core Write is built on, and it is a setting you choose once and forget. The point of it is simple: an interface that suits your eyes and your room, with a page that always shows the real document.
Whichever theme you choose, your files are not affected. Theme is a setting for the app, not for the document. A letter written in dark mode prints and exports exactly the same as one written in light mode, and someone opening your .docx in another word processor sees nothing different.