The real effect comes from microscopic ridges diffracting light, but on the web it's faked by layering multiple colour conic/linear-gradients and compositing them onto the base surface with mix-blend-mode: color-dodge.
Shifting the gradient's angle with the pointer (or device tilt) makes the shimmer visibly travel as the "card" tilts — selling the illusion of a real holo card.
When to use
Use for promo cards, limited-edition badges, game item cards. If there’s text, colours shifting underneath hurt legibility — back it with a dark plate.