Yeah! as @MLFromScratch and @DavidDarnes said we have to modify the CSS file,
Now it’s working fine for me. 
My bad! I was misunderstood. we don’t need to remove everything.
Just remove @media (prefers-color-scheme: dark) and { } that’s it.
I edited css from both paths /assets/built/screen.css & /assets/css/screen.css
Thanks again ,
@DavidDarnes
@MLFromScratch
@vikaspotluri123
@giacomosilli