This doesn't seem to be a specific skin problem, I can reproduce it in Timeless and Vector.
- Open any module editing page, like https://zh.wikipedia.org/w/index.php?title=Module:Citation/CS2&action=edit.
- Click on the gray textarea of the Debug console.
A colored border appears, but the textarea does not display the caret, which makes it look like a read-only standard output terminal, which once misled me.