How to add a sound effect to default buttons.

Hello all. I just started using sugarcube 2 and I'm not sure how to add sound effects to the default menu buttons (Save, Restart and the "Hide UI bar" button specifically). I'm able to do this for the regular buttons in the StoryMenu passage by populating it with the following: e.g.:
<<click "Inventory">><<audio "click" stop>><<audio "click" play>><<goto "Inventory">><</click>>

But I can't figure out where I should do this for the default bu