VSCode: minimizing button disappears?

I’m using VSCode. Sometimes, the expansion/minimization buttons in the upper right corner disappear:

and I don’t know how to get out of VSCode… the only way I have found is to kill the VSCode app using the task list (Ctrl+Shift+Esc).

I assume that I have accidentally toggled a mode of VSCode by some accidental keyboard combination.

  • Is this a bug or a feature?
  • Is there a keyboard combination to get back the minimization/expansion buttons in the above image (including “x”)?