I am encountering what appear to be 3 bugs connected with the use of a Region Display Selector region in APEX 21.1.
These are demonstrable on apex.oracle.com.
The unselected regions are momentarily visible on page load.
The focus outline styling is obtrusive, ugly, and missing the top of the rectangle (and the left edge when the first tab has focus).
When the regions are not positioned in the first column, on selecting any region but the first, an increasingly large gap appears between the bottom of the RDS region and the top of the displayed region.
macOS 11.4
Safari 14.1.1
Chrome 92.0.4515.69 (doesn't show focus issue)
Firefox 89.0.1