playground: align button on left

[aspeddro]

#691

[ryyppy]

Mh... the alignment is a little weird. So either we move it like this:

So that the buttons start at least on the same level as the code / after the gutter.

Ideally it should be here, but not sure how this would interact with the resizable sidebar:

[aspeddro]

It is possible to integrate with resizable divider, but this format makes it easier to calculate the height of the editor panel.