When I reveal the playground console output, the grey 1 pt divider lines between the three text areas (Editor, Playground, and Console) become almost impossible to click and drag.
It seems to me their hit area is also exactly 1 pt wide when both sides contain a text area. The divider line has a somewhat wider hit area only when it's next to a non-text entry UI element such as line numbers.
I think it would make sense to increase the hit area width to at least 5 pt (i.e. line width ± 2 pt), or consider adding a drag handle that maybe appears when hovering mouse near the divider line.