.bubble {
	position: absolute;
	width: 50px;
	height: 50px;
	background-image: url("../images/bubble_sprite_sheet.png");
}
.cur_bubble {
	left: 360px;
	top: 470px;
}
.bubble_0 {
	background-position: 0 0;
}
.bubble_1 {
	background-position: 0 -50px;
}
.bubble_2 {
	background-position: 0 -100px;
}
.bubble_3 {
	background-position: 0 -150px;
}