I do not qute understand what behaviour you want?
#My calculator
fickle mesa
(and on clear you might set the display to 0perhaps)
the entire container of the calculator?
you can add a class like '.expand' to the button when clicked, set a the dimensions in css on clearBtn.expand
while having the original dimensions on 'clearBtn' and a dd a transition for the attributes which get changed.
How exactly depends on your structure and CSS
okay then you can set the taget dimensions there and add the transition(for the clear button only)