向下滚动加载元素动画效果

fade
fade-up
fade-down
fade-left
fade-right
fade-up-right
fade-up-left
fade-down-right
fade-down-left
flip-up
flip-down
flip-left
flip-right
slide-up
slide-down
slide-left
slide-right
zoom-in
zoom-in-up
zoom-in-down
zoom-in-left
zoom-in-right
zoom-out
zoom-out-up
zoom-out-down
zoom-out-left
zoom-out-right