the last parameter "ease" is the name of a function that controls the speed of the transition.
It supports various predefined functions such as "ease", "ease-in", "ease-out", "ease-in-out", "linear"
And you can also define your own transition speed using something called a "Cubic Bezier". It is a very complicated thing to understand but very easy to use, there are several online generators that will give you what you need such as http://cubic-bezier.com/ https://matthewlein.com/ceaser/