Linux (dark system theme): code completion is hard to read

I'm on Manjaro Linux (Gnome edition, GTK 3.24.36) which uses a dark theme by default ("Adw-dark"). As shown in the screenshot below, the code completion popup uses colors where foreground (middle gray) and background (middle blue) have a very bad contrast and hence are even for users with reasonable eyes hard to read.
Setting GTK_THEME=Adwaita before launching Eclipse fixes the problem, but it looks like an alien application (white theme while the system is dark).

The issue identifies the code completion popup in Eclipse on Manjaro Linux with the Adw-dark GTK theme, but names no source file or test. First reproduce the contrast problem under the dark system theme and compare it with GTK_THEME=Adwaita; done means the completion popup is readable without switching to a light theme.

Written by the indexing model from the issue text.