Offer an overlay for all pop-ups
It's a UX/Ui tweak from Nick Kolenda: https://www.nickkolenda.com/user-experience/#ux-strategy5
This should be relatively simple: Place each modal in a wrapper div and give this div a background color with alpha channel.
However, use some animation effects. There are tons of CodePens (search for "Overlay modal"), e. g. this one:
For styling offer SaaS variables: