Opacity
opacity 属性指定了一个元素的不透明度。换言之，opacity 属性指定了一个元素后面的背景的被覆盖程度。
语法
| Class | 属性 |
|---|---|
| opacity-0 | opacity: 0; |
| opacity-5 | opacity: 0.05; |
| opacity-10 | opacity: 0.1; |
| opacity-15 | opacity: 0.15; |
| opacity-20 | opacity: 0.2; |
| opacity-25 | opacity: 0.25; |
| opacity-30 | opacity: 0.3; |
| opacity-35 | opacity: 0.35; |
| opacity-40 | opacity: 0.4; |
| opacity-45 | opacity: 0.45; |
| opacity-50 | opacity: 0.5; |
| opacity-55 | opacity: 0.55; |
| opacity-60 | opacity: 0.6; |
| opacity-65 | opacity: 0.65; |
| opacity-70 | opacity: 0.7; |
| opacity-75 | opacity: 0.75; |
| opacity-80 | opacity: 0.8; |
| opacity-85 | opacity: 0.85; |
| opacity-90 | opacity: 0.9; |
| opacity-95 | opacity: 0.95; |
| opacity-100 | opacity: 1; |