/*WebKit browsers*/
input::-webkit-input-placeholder {
color: #666 !important;
}
/*Mozilla Firefox 4 to 18*/
input:-moz-placeholder {
color: #666 !important;
}
/*Mozilla Firefox 19+*/
input::-moz-placeholder {
color: #666 !important;
}
/*Internet Explorer 10+*/
input:-ms-input-placeholder {
color: #666 !important;
}
参考文献:https://www.jianshu.com/p/8f17298d7d2f