opacity 用于指定元素透明度, 支持 0~1 之间的小数.
默认值 1-完全不透明, 0-完全透明
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>opacity</title><style>/*opacity默认 1, 完全不透明0 完全透明*/.box1 {width: 100px;height: 100px;background-color: #FF9500;position: fixed;z-index: 11;/*半透明*/opacity: .5;}.box2 {width: 100px;height: 100px;background-color: #0f88eb;position: fixed;left: 33px;top: 33px;z-index: 9;opacity: .5;}.box3 {width: 100px;height: 100px;background-color: #A1D8AD;position: fixed;left: 66px;top: 66px;z-index: 8;opacity: .5;}</style></head><body><div class="box1"></div><div class="box2"></div><div class="box3"></div></body></html>
