Completely useless. It just darkens the toolbar in Sheets. Not the cells.

Does not work in 2021

Sí cambia el estilo y algunos elementos, pero no de una forma buena o útil. No cumple con su función de facilitar la lectura/uso, pero la idea es muy buena.

Only partially modifies the styling, but does it very poorly. Seems to be partially broke as of now, some parts are white, fonts have weird red/blue anti-aliasing... Not usable imo.

I used this for over a year and suddenly, it doesn't work properly any more. It was really nice to use and I liked using it even when writing during the day. But, now only the ribbon and the page will be dark, the background around the actual document is still white, so it is still too bright and is now useless. I have uninstalled other extensions to see if that was causing issues, I tried removing and re-adding this extension and it never fixed it. Shame, I liked it better than other dark mode extensions, but now it's too broken for me to use.

It turns most sections black, but this causes issues in other areas, such as in the font section and other areas.

Looks good for basic editing, but many things need polishing:
- highlighted text only has thin blue lines above and below. I suspect this is not intentional, just a boxing artefact
- when suggesting changes, suggestins are completely invisible while being edited
- menus are still white
- turning light mode back on doesn't restore the original css and many things look out of place. E.g. comment boxes still have a grey background

Certain things are a bit tricky to read but apart from that it's great.

This is a fine enough add-on but some elements, (like the document title) don't look the greatest. Other than that, it's great for some late night writing or finishing that essay that's due in 3 hours.

works well, the ease of swapping between dark and light is nice

A good dark theme isn't 100% black. Also it blacks out the document background too and has zero options.

As many others have said, it kind of screws with the backgrounds of icons and the document name is strange, but it does give a dark mode, so I plan to use it nonetheless. Improvements would be appreciated!

Makes the name and buttons harder to see but I appreciate the dark mode.

The panel looks bad

Does what it says, however I found that it removes the cursor for me, on Windows 10 Firefox 74. Unfortunately, due to this flaw, I can't continue to use it.

I'm using this on a Mac OS machine (10.14) and I don't have the problem with the cursor disappearing when switching back to lightmode. However the name of the doc and the icons are pretty much unreadable. But the overall rest my eyes have from this is worth that minor quibble.