Notices problems are
- Links in content area are higher (in terms of z value) than the sticky header.
- The sidebar header for table of contents seems to be positioned higher than it should.
- Text size of breadcrumb and title are too big.
- Flickering problem on pages that are short (less content/one page content).
Using debouncing idea described in
https://css-tricks.com/styling-based-on-scroll-position/ to record
scrollY value and render the `BoxedTitle` base on the value. The box is
hidden when scrollY is greater than 30.
The class-style React component is used to register an event listener
for scrolling event.
jumpyapple