<input type="text" class="form-control" placeholder="測試內容">
::placeholder { /* Chrome, Firefox, Opera, Safari 10.1+ */
  color: red;
  opacity: .4;
}

:-ms-input-placeholder { /* Internet Explorer 10-11 */
  color: red;
}

::-ms-input-placeholder { /* Microsoft Edge */
  color: red;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.