Placeholder support for contentEditable elements, without JavaScript

All you need is to add the following CSS:

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

Notes

• Can add a different style than actual text like opacity, italic, etc
• If your html needs to be 100% compliant, you can replace "placeholder" for "data-placeholder" on both files
• Chrome will add <br />'s inside contentEditable elements in some cases, breaking the :empty check. Can be fixed with a bit of JavaScript.
• pointer-events: none is there so the cursor is the right one when hovering