RStudio 1.1.383 No scroll bars when choosing light-colored Editor theme

I am using RStudio Version 1.1.383 and when I change the Editor theme to a light-colored theme (e.g., Clouds, then the vertical scrollbar in the Environment pane and the horizontal scrollbar in the script pane disappear! They return when I simply apply a dark-colored theme (e.g, Chaos). Why?

The scrollbars returned when I switched the RStudio theme to "Classic" (was on "Modern").