Change opacity of non-featured slides in Banner Slideshow

Password to view the site is Memphis#1

I am wanting to set the opacity (to .5) for the images to the left and right of center, so the main image is visible fully, with a hint of what's to the left and right, and can't work out how to do it via CSS. This page will eventually have several Banner Slideshows, so a solution is as durable as possible would be much appreciated.

Can you share your website URL?

Oh, sorry: https://jdcaldwellarchitect.squarespace.com/ 

Password: Memphis#1