Fix to use offsetTop of absolute positioned container element

[mindfull]

Hello,

I had been suffered from scroll offset error, and I've finally found scrollOffset function in modules/mixins/utils.js is not working properly when container is absolute positioned element.

I'm actually using react-custom-scrollbars to customize scrollbars, and it makes container element as an absolute positioned element. Because the computed position property of the container element is not relative but absolute, scroller changes scrollTop to wrong position.

I tried to change 26th line of modules/mixins/utils.js from

      t.getBoundingClientRect().top + (window.scrollY || window.pageYOffset) : getComputedStyle(c).position === "relative" ? t.offsetTop : (t.getBoundingClientRect().top + c.scrollTop)

to

      t.getBoundingClientRect().top + (window.scrollY || window.pageYOffset) : getComputedStyle(c).position !== "static" ? t.offsetTop : (t.getBoundingClientRect().top + c.scrollTop)

and all of my problem is gone.

** In addition, I also tested this changes for fixed positioned container element, it worked properly.

[fabioberger]

I had the same issue, but my container div was absolutely positioned, so I had to change this to "absolute". Are these just missing edge-cases @fisshy, or are we doing something wrong?