The table of contents in `javadoc`-generated API documentation keeps track of vertical offset of elements in the current page in order to highlight the currently viewed element. Page offsets are updated when the size of the browser changes, but not when the size of the document body changes for other reasons, such as selecting a subgroup of methods in the "Method Summary" table of a class or interface.

Instead of just handling changes in browser size, we should handle all changes of size of the document body element. This can be done by using the ResizeObserver API[1] which has been implemented in all supported browsers for several years.

[1]: https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver