This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.


The :-moz-only-whitespace CSS pseudo-class matches an element that has no child nodes at all or empty text nodes or text nodes that have only white-space in them. Only when there are element nodes or text nodes with one or more characters inside the element, the element doesn't match this pseudo-class anymore.


span:-moz-only-whitespace { style properties }



span:-moz-only-whitespace::before {
  background-color: lime;


<span> </span>

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 Contributors to this page: Sebastianz, teoli, Sheppy, ethertank, Marsf, Fredchat, Mw22
 Last updated by: Sebastianz,