How to make in slider navigation similar “filling” navigation item?

Question

JavaScript

How to make slider navigation similar to "fill" navigation item in slick.js?
There is a certain time during which the scroll to the next slide is carried out, and during this time the slightly transparent block near the navigation "fills up".
Link to example: https://www.oneplus.com/en/brand?from=foot

Answer 1

https://codepen.io/fallus/pen/BaybNxG
In general, I'm a designer.