One of the trending UX features right now is dark mode. According to one study, 58% of Americans experience digital eye strain from using computers. One of the factors causing it is blue light radiation from the screen. That's where the possible idea of a screen that slows down your tired eyes more comes from.
Windows, as one of the biggest consumer desktop platforms, does not escape the dark mode feature. Since Windows 10, dark mode can be enjoyed by its users. Unfortunately, LibreOffice which is on the GNU/Linux platform has remarkable stand at following this trend thanks to its ability to blend in with system themes which has been a bitter pill to swallow over the past few years.
Let's say huge thanks to Caolán McNamara, one of the LibreOffice developers from Redhat who is usually on the UX/UI side of improving LibreOffice integration with GTK, for sending a patch so that LibreOffice for Windows can now enjoy dark mode.
Actually, this article wants to discuss the presence of the dark variant of the Colibre icon theme, but somehow after I sent the dark variant of the Colibre theme patch to the core, Caolán actually fulfilled the expectations of many years later.
Basically, apart from following the interface of the system in which it is installed, LibreOffice supports custom themes via Firefox personas, but unfortunately not all parts of the interface are changed with this Firefox persona. Only the standard toolbar can be themed, while the sidebar let alone the tabbed UI are completely untouched.
Half-hearted theme:
It getting worse with Tabbed UI:
Initially I wanted to make this Colibre variant dark icon theme as a trigger so that the dark mode in Windows is immediately materialized. It turned out that not long after that my wish was granted. To enable it, first thing first you must enable dark mode in OS level, then in LibreOffice, enable experimental features in Tools >
Options > LibreOffice > Advanced. Check "Enable experimental
feature (may be unstable)". LibreOffice will ask for restart and then automatically switch the UI to dark mode along with Colibre dark icon after restart.
Here is what dark mode looks like on my Windows 11. 
The Start Center looks very promising, the title bar got dark also.