placeholder样式的修改

::-webkit-input-placeholder {
  /* WebKit, Blink, Edge */
  color: #b3b3b3;
}
:-moz-placeholder {
  /* Mozilla Firefox 4 to 18 */
  color: #b3b3b3;
}
::-moz-placeholder {
  /* Mozilla Firefox 19+ */
  color: #b3b3b3;
}
:-ms-input-placeholder {
  /* Internet Explorer 10-11 */
  color: #b3b3b3;
}