CSS - ::selection

Gecko is the only engine requiring the prefix. Due to the fact that the CSS parsing rules require dropping the whole rule when encountering an invalid pseudo-element, two separate rules must be written: ::-moz-selection, ::selection {...}. The rule would be dropped on non-Gecko browsers as ::-moz-selection is invalid on them.

HTML

<div>This is some text for you to test CSS's ::selection pseudo-class.</div>
<p>Also try to select some text in this &lt;p&gt;</p>

CSS

/* draw any selected text yellow on red background */
::-moz-selection {
  color: gold; background: red;
}

::selection {
  color: gold; background: red;
} 

/* draw selected text in a paragraph white on black */
p::-moz-selection {
  color: white;
  background: black;
}

p::selection {
  color: white;
  background: black;
}

Output