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/* In HTML */
<div contenteditable="true" placeholder="This is a placeholder"></div>
/* In CSS */
[contenteditable=true]:empty:before {
content: attr(placeholder);
color: #757575;
pointer-events: none;
}
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[contenteditable=true]:empty:before{
content: attr(placeholder);
pointer-events: none;
display: block; /* For Firefox */
}