Heading into the Twitter PWA as normal, it automatically switches to night mode, picking up my system theme in this case; (right) note the manual toggles for night mode and also 'Data saver', restricting the media content shown inline.
Twitter PWA is also a 'Share' target these days, so you can share to it from other applications under Windows 10 Mobile; (right) Tweeting away (as part of a share from Edge), note the newish 280 character circle indicator, top right. This fills up as you type....
As I commented before:
It does the job, but it's not battery efficient and there's no integration with Action Center. Can notifications be somehow added in a way that's compatible with Windows 10 Mobile Edge? I'm not so sure. Which is why this is definitely a downgrade for most people.
You can grab or update the Twitter PWA-ified UWP client here in the Store. Enjoy night mode and enjoy the 280 character compatibility, but it's still not a patch on the commercial third party client, Tweetium UWP, which offers every feature under the sun, right up to push notifications, and which I've been recommending for the last couple of years.