Keep selection visible when blurred (focus in a panel)

How can I keep the selection visible when the focus moves away from the editor? seem to have done it successfully so I guess it can be done.

I have a panel at the bottom with a textfield that displays the row:col position of the cursor.
When this gets the focus, then the selection in the editor becomes invisible.
Calling focus() on cm-content brings it back, but I don’t know how to make it stay when the editor is blurred.
I thought this might be my theme, but I tried with the OneDark theme and it does the same.
I’d appreciate some guidance on how to achieve this.

(I have a repl with the code here).

Thank you

I found my answer in the doc. I needed to use the drawSelection extension.