Decrease contrast in Manjaro

I was trying to decrease contrast in Manjaro system like we do for photo editing. Screenshot from 2021-08-24 00-14-35

I can decrease contrast for websites using Dark Reader extension in Chrome. But, it’s not helpful for Document Viewer (PDF viewer). I was searching in Settings if there’s a way to decrease contrast. I just found high contrast nothing else.

You can probably do it using DisplayCAL. I personally use DisplayCAL with a colorimeter though, never tried it manual.

How can I?

I can’t understand what I should do…