SOLVED(almost) Via Addon (for OPERA)
although its not perfect.. but works

here is how it looks


you need to add this Extension to opera
https://addons.opera.com/en/extensio...ls/night-mode/

the addon adds a tiny button on upper right(next to search) to quick switch night mode)


but, if you reload or open another tab its again Normal Mode


Note - there's difference in appearance between Addon's result and permanent one(if you look closely)