改变input标签中placeholder显示的颜色

::-webkit-input-placeholder { /* WebKit browsers */
    color:    #A9A9A9;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
   color:    #A9A9A9;
   opacity:  1;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
   color:    #A9A9A9;
   opacity:  1;
}
:-ms-input-placeholder { /* Internet Explorer 10+ */
   color:    #A9A9A9;
}
::-webkit-input-placeholder { /* WebKit bro