Zend certified PHP/Magento developer

How to change the color of a portion of the screen? [closed]

I want to use slop to select a portion of the screen, and I would like to highlight that portion somehow. Some screenshot softwares have it already like https://github.com/flameshot-org/flameshot , where the whole screen except the highlighted portion is covered with black color. I am wondering if this behavior can be replicated using a tool.

EDIT: Not sure why this got closed. I am not requesting a recommendation. I have a problem that I want to solve, and I tried to search for solutions, but I didn’t find something relevant. My searches lead me to screen linux command (because I tried to use the term screen while searching), or a compistor softwares like picom, or annotation softwares like gromit-mpx.