All browsers + IE9 Show archive.org snapshot know the CSS :empty selector. It lets you hide an element when it has no content, i.e. not even white space.

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(How to prevent whitespace in HAML) Show archive.org snapshot

For instance, you have a badge displaying the number of unread messages in a red bubble with white text:

.unread-messages-bubble {
  background-color: red;
  border-radius: 10px;
  padding: 10px;
  color: white;
}

To hide that bubble entirely when there are no new messages:

.unread-messages-bubble:empty {
  display: none;
}

Note that the element must be completely empty for :empty to match.
See DevDocs Show archive.org snapshot .