什么是透明度？
透明度分为256个等级，即 0 ~ 256 之间的取值，0 表示完全透明，255 表示完全不透明。
透明度 0 (完全透明) –> 255 (完全不透明)对应的 16 进制是 00 (完全透明) –> FF (完全不透明)。
如: 50% 透明度的 50% 是 256 的一半即 128，因为是从 0 开始算的，所以是 127，转换成 16 进制就是 7F。
注意：透明度 和 不透明度 是两个概念，它们加起来是1，或者100%
透明度对应的十六进制值(00[完全透明]；FF[完全不透明])
| 透明度 | 16进制值 | 透明度 | 16进制值 | 透明度 | 16进制值 |
|---|---|---|---|---|---|
| 100% | 00(完全透明) | 66% | 57 | 32% | AD |
| 99% | 03 | 65% | 59 | 31% | B0 |
| 98% | 05 | 64% | 5C | 30% | B3 |
| 97% | 07 | 63% | 5E | 29% | B5 |
| 96% | 0A | 62% | 61 | 28% | B8 |
| 95% | 0D | 61% | 63 | 27% | BA |
| 94% | 0F | 60% | 66 | 26% | BD |
| 93% | 12 | 59% | 69 | 25% | BF |
| 92% | 14 | 58% | 6B | 24% | C2 |
| 91% | 17 | 57% | 6E | 23% | C4 |
| 90% | 1A | 56% | 70 | 22% | C7 |
| 89% | 1C | 55% | 73 | 21% | C9 |
| 88% | 1E | 54% | 75 | 20% | CC |
| 87% | 21 | 53% | 78 | 19% | CF |
| 86% | 24 | 52% | 7A | 18% | D1 |
| 85% | 26 | 51% | 7D | 17% | D4 |
| 84% | 29 | 50% | 80 | 16% | D6 |
| 83% | 2B | 49% | 82 | 15% | D9 |
| 82% | 2E | 48% | 85 | 14% | DB |
| 81% | 30 | 47% | 87 | 13% | DE |
| 80% | 33 | 46% | 8A | 12% | E0 |
| 79% | 36 | 45% | 8C | 11% | E3 |
| 78% | 38 | 44% | 8F | 10% | E6 |
| 77% | 3B | 43% | 91 | 9% | E8 |
| 76% | 3D | 42% | 94 | 8% | EB |
| 75% | 40 | 41% | 96 | 7% | ED |
| 74% | 42 | 40% | 99 | 6% | F0 |
| 73% | 45 | 39% | 9C | 5% | F2 |
| 72% | 47 | 38% | 9E | 4% | F5 |
| 71% | 4A | 37% | A1 | 3% | F7 |
| 70% | 4D | 36% | A3 | 2% | FA |
| 69% | 4F | 35% | A6 | 1% | FC |
| 68% | 52 | 34% | A8 | 0% | FF(完全不透明) |
| 67% | 54 | 33% | AB |
不透明度 alpha 对应的十六进制值(FF[完全不透明]；00[完全透明])
计算方法：255 * 不透明度 —> 转换成 16 进制
例：30% 不透明度的计算方式：255 * 30% = 76.5，四舍五入 77，转为 16 进制为 4D
注：alpha 是 rgba() 中的 a 值 [r: 红色, g: 绿色, b: 蓝色, a: alpha值]
rgb 的取值范围在 0~255 之间，a 的取值范围在 0~1 之间(可以是小数)
a 值规定色彩的透明度：0; 完全不透明, 0.5: 半透明, 1: 完全透明
| 不透明度 | 16进制值 | 不透明度 | 16进制值 | 不透明度 | 16进制值 |
|---|---|---|---|---|---|
| 100% | FF(完全不透明) | 66% | A8 | 32% | 52 |
| 99% | FC | 65% | A6 | 31% | 4F |
| 98% | FA | 64% | A3 | 30% | 4D |
| 97% | F7 | 63% | A1 | 29% | 4A |
| 96% | F5 | 62% | 9E | 28% | 47 |
| 95% | F2 | 61% | 9C | 27% | 45 |
| 94% | F0 | 60% | 99 | 26% | 42 |
| 93% | ED | 59% | 96 | 25% | 40 |
| 92% | EB | 58% | 94 | 24% | 3D |
| 91% | E8 | 57% | 91 | 23% | 3B |
| 90% | E6 | 56% | 8F | 22% | 38 |
| 89% | E3 | 55% | 8C | 21% | 36 |
| 88% | E0 | 54% | 8A | 20% | 33 |
| 87% | DE | 53% | 87 | 19% | 30 |
| 86% | DB | 52% | 85 | 18% | 2E |
| 85% | D9 | 51% | 82 | 17% | 2B |
| 84% | D6 | 50% | 80 | 16% | 29 |
| 83% | D4 | 49% | 7D | 15% | 26 |
| 82% | D1 | 48% | 7A | 14% | 24 |
| 81% | CF | 47% | 78 | 13% | 21 |
| 80% | CC | 46% | 75 | 12% | 1F |
| 79% | C9 | 45% | 73 | 11% | 1C |
| 78% | C7 | 44% | 70 | 10% | 1A |
| 77% | C4 | 43% | 6E | 9% | 17 |
| 76% | C2 | 42% | 6B | 8% | 14 |
| 75% | BF | 41% | 69 | 7% | 12 |
| 74% | BD | 40% | 66 | 6% | 0F |
| 73% | BA | 39% | 63 | 5% | 0D |
| 72% | B8 | 38% | 61 | 4% | 0A |
| 71% | B5 | 37% | 5E | 3% | 08 |
| 70% | B3 | 36% | 5C | 2% | 05 |
| 69% | B0 | 35% | 59 | 1% | 03 |
| 68% | AD | 34% | 57 | 0% | 00(完全透明) |
| 67% | AB | 33% | 54 |