Popover / Dropdown Open

A dialog fades in while scaling up slightly from its center over a dimmed page.

Add a "Modal Scale-Fade In" animation (also called a dialog open animation or zoom-fade dialog) to [where].
The dialog should fade in while scaling up slightly from its center as the page behind it dims: quick and subtle, with no bounce.
Play it once each time the dialog opens, move focus into it and keep it there, and use a plain fade for users who prefer reduced motion.

A small label fades and nudges into place next to an element after a short hover delay.

Add a "Tooltip Fade" (also called a tooltip reveal) to [where].
After a short hover delay, the label should fade in while nudging slightly into place next to the element, then disappear quickly with no delay when the pointer leaves.
Show it on keyboard focus too, let Escape dismiss it, and connect it to the element so screen readers read it.

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 content panel smoothly grows to its full height or shrinks to zero when its header is toggled.

Add an "Accordion Expand-Collapse" effect (also called a collapse or disclosure) to [where].
When a header is pressed, its panel should smoothly grow to the full height of its content and shrink back to nothing on the next press, with the header's arrow turning to match: quick and smooth, no bounce.
Animate to the content's real height rather than a fixed guess, keep the header a real button that exposes its expanded state, and make it work from the keyboard.

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.

A brief message slides or fades in at a screen edge, waits, then leaves; stacked toasts shift to make room.

Add a "Toast Slide-In" (also called a snackbar or toast notification) to [where].
Each message should slide up from the screen edge and fade in, decelerating smoothly; when a new toast arrives, the ones already shown should shift over smoothly to make room.
Announce the message to screen readers without stealing focus, keep it up long enough to read, and pause the auto-dismiss on hover or focus.