Animated Background

# Animation pattern — Animated Background

Visually highlights selected items by sliding a background into view when hovered over or clicked. This smooth transition helps users focus on the active item, making it ideal for interactive lists, menus, or navigations where clear selection feedback is important.

Build it in React with `motion` (motion/react) and Tailwind CSS. Respect `prefers-reduced-motion` (render the final state without movement), keep it under ~400 ms for UI feedback, and animate only transform and opacity where possible.

Reference implementation (Motion-Primitives, MIT):

```tsx
'use client';
import { cn } from '@/lib/utils';
import { AnimatePresence, Transition, motion } from 'motion/react';
import {
  Children,
  cloneElement,
  ReactElement,
  useEffect,
  useState,
  useId,
} from 'react';

export type AnimatedBackgroundProps = {
  children:
    | ReactElement<{ 'data-id': string }>[]
    | ReactElement<{ 'data-id': string }>;
  defaultValue?: string;
  onValueChange?: (newActiveId: string | null) => void;
  className?: string;
  transition?: Transition;
  enableHover?: boolean;
};

export function AnimatedBackground({
  children,
  defaultValue,
  onValueChange,
  className,
  transition,
  enableHover = false,
}: AnimatedBackgroundProps) {
  const [activeId, setActiveId] = useState<string | null>(null);
  const uniqueId = useId();

  const handleSetActiveId = (id: string | null) => {
    setActiveId(id);

    if (onValueChange) {
      onValueChange(id);
    }
  };

  useEffect(() => {
    if (defaultValue !== undefined) {
      setActiveId(defaultValue);
    }
  }, [defaultValue]);

  return Children.map(children, (child: any, index) => {
    const id = child.props['data-id'];

    const interactionProps = enableHover
      ? {
          onMouseEnter: () => handleSetActiveId(id),
          onMouseLeave: () => handleSetActiveId(null),
        }
      : {
          onClick: () => handleSetActiveId(id),
        };

    return cloneElement(
      child,
      {
        key: index,
        className: cn('relative inline-flex', child.props.className),
        'data-checked': activeId === id ? 'true' : 'false',
        ...interactionProps,
      },
      <>
        <AnimatePresence initial={false}>
          {activeId === id && (
            <motion.div
              layoutId={`background-${uniqueId}`}
              className={cn('absolute inset-0', className)}
              transition={transition}
              initial={{ opacity: defaultValue ? 1 : 0 }}
              animate={{
                opacity: 1,
              }}
              exit={{
                opacity: 0,
              }}
            />
          )}
        </AnimatePresence>
        <div className='z-10'>{child.props.children}</div>
      </>
    );
  });
}
```