h5修改input placeholder 颜色

::-webkit-input-placeholder {
/* WebKit browsers */
color: #999;
}
:-moz-placeholder {
/* Mozilla Firefox 4 to 18 */
color: #999;
}
::-moz-placeholder {
/* Mozilla Firefox 19+ */
color: #999;
}
:-ms-input-placeholder {
/* Internet Explorer 10+ */
color: #999;
}