Build a Website

I am building a website and would like a simple animation of a small black box moving along a white line. Imagine a white line that is hilly (the line is not just straight, it moves up and down, similar to what a rollercoaster would look like from a side view) and a black box that is animated using simple CSS to travel along the white line and reach a stopping point. When the page initially loads, the black box should be stationary and then, when the users scrolls down, the black box should travel along the white line and reach a stop at the end of the line.