Review how VS Code applies high contrast colors https://code.visualstudio.com/api/references/theme-color#contrast-colors and apply them similarly in Theia.
We leave it out from the initial theming.
Some issues are also listed here: https://github.com/eclipse-theia/theia/issues/7353
Explorer,The context menu, in the browser example, is also broken:


In the Problems View, there is no border around the selected node.
In VS code,

In Theia,

(Arrow pointing to the selected node)
Editor and Explorer decorators always white with the HC theme. I would expect red and yellowish colors.

Support for hover. VS Code:

TODO: Revisit whether we want to support it for dialog buttons or not. VS Code does not have any dialogs but they do not support it in the Explorer:

Difference between the editor error markers:
VS Code

Theia:

Maybe it is a TS issue.