The CSS Transition component

Then we need to apply transition to each element. Inside the map we put what is depicted by the image. The CSSTransition component is the first element that comes from the map function and wraps everything within.

We put the key property because the CSSTransition component is the first outer element of the map function. The timeout specifies after how many milliseconds each list item will be mounted and unmounted to and by the DOM. Last but not least we give a className to the classNames attribute.