透明度参照表：
00%=FF（不透明） 5%=F2 10%=E5 15%=D8 20%=CC 25%=BF 30%=B2 35%=A5 40%=99 45%=8c 50%=7F
55%=72 60%=66 65%=59 70%=4c 75%=3F 80%=33 85%=21 90%=19 95%=0c 100%=00（全透明）
css背景渐变效果兼容：
background: -webkit-gradient(linear, 0 0, 100% 0, from(rgba(0,0,0,0.2)), to(rgba(255,255,255,0.8)));/*chrome*/
background: -moz-linear-gradient(left, red, blue); /*firefox*/
filter: progid:DXImageTransform.Microsoft.gradient(gradientType=1,startColorstr=#bf000000, endColorstr=#bfFFFFFF); /* IE6,IE7 */
-ms-filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='rgba(0,0,0,0.2)', endColorstr='rgba(255,255,255,0.8)'); /* IE8 */