I created a horizontal collage of photos, and I want to change the opacity so the collage / gallery blends in with the background. There currently is not an option in the Wix settings except for individual images not in a gallery or single background images -- anyone know of code for this?

I coded my gallery so it will filter images with the click of a button (by category). What I cannot figure out is how to make the images move a certain way, such as fly effects, when they filter. Example website here whose filtering effects I want to replicate: https://www.effekt.dk/work/# Notice how the images move on the page. My filter settings currently have images or galleries 'appear' rather than images flying or moving to their category. Anybody know how to do this?? Thanks!