<div contenteditable="true" placeholder="何か入力してみてください"></div>
/*by https://codepen.io/flesler/pen/AEIFc */

[contenteditable=true]:empty:before{
  content: attr(placeholder);
  pointer-events: none;
  display: block; /* For Firefox */
}



div[contenteditable=true] {
  border: 1px dashed #AAA;
  width: 290px;
  padding: 15px;
}

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