Max size of scrollbar thumbs

[mathsgod]

Motivation

In some of the design, I need to limit the scrollbar thumb max size. For example, I need to change the thumbs shape to circle.
For the current version, if I change thumbs size using css (say fixed 10px), the thumbs will be wrong position when scroll to the bottom.

I know it is because the thumbs offset are updated after render using

\\thumb.ts
 this.offset = scrollOffset / pageSize * (containerSize + (this.realSize - this.displaySize));

Proposal

In the options, provide thumbMaxSize parameter to allow set to thumb max size.