關 – Guan1 – Close, Shut, Turn Off, Concern, Involve
So open is 開 and close is 關. They look similar. The frame around both is 門 – Men2 – Door.
Inside 開 is 幵 – Jian1 – Even, and inside 關 is something meaningless and confusing, but it seems to have something to do with threads or looms.