Modal Scale-Fade In

A floating menu fades and scales in from the point where its trigger sits.

Add a "Popover / Dropdown Open" animation (also called a menu pop or dropdown scale-fade) to [where].
The menu should fade in while growing slightly out of the corner next to its trigger, quick and crisp, and fade out a little faster when it closes.
Keep it anchored to the trigger, close it with Escape or a click outside, and expose the open state on the trigger for screen readers.

The element grows from a small, transparent state to full size while fading in.

Add a "Zoom In" entrance animation (also called scale in) to [where].
The element should grow from small and transparent to full size while fading in: quick and smooth, with no overshoot.
Scale it from its center without affecting the surrounding layout, and show it in place without motion when the user prefers reduced motion (prefers-reduced-motion).

A thumbnail scales up from its place into a large centered view over a dimmed backdrop.

Add a "Lightbox Zoom" (also called an image zoom overlay or Medium-style zoom) to [where].
Clicking a thumbnail should make it grow smoothly from its own place into a large centered view while the page behind fades back, and closing should shrink it back into the same place.
Close it with Escape or a click on the backdrop, move focus into the view while it is open, and return focus to the thumbnail afterward.

A translucent dark layer fades in behind an overlay to dim the page.

Add a "Backdrop Scrim Fade" (also called an overlay fade or scrim) to [where].
When the overlay opens, a translucent dark layer should fade in softly over the page behind it, a little slower than the overlay itself, and fade out again when it closes.
Keep the scrim dark in both light and dark themes, and stop the page behind it from scrolling or taking clicks while it is shown.

An element appears to move and resize into a matching element in a new spot, sharing one identity.

Add a "Shared Layout Animation" (also called an in-page shared element) to [where].
When the selection changes, the element should appear to move and resize smoothly from its old spot into its new one, easing gently into place, so it reads as one object rather than two.
Show only one copy at any moment, and keep the surrounding layout from jumping while it moves.

An underline or pill glides from the old tab to the newly selected tab.

Add a "Tab Indicator Slide" (also called a sliding underline or active tab indicator) to [where].
When a new tab is selected, the underline should glide from the old tab to the new one, quick and smoothly decelerating, stretching to the new tab's width if it differs.
Keep proper tab semantics with arrow-key navigation, and move the indicator without sliding for users who prefer reduced motion.