<ul>
  <li data-pseude-content="1 - ">First element</li>
  <li data-pseude-content="2 - ">Second element</li>
  <li data-pseude-content="3 - ">Third element</li>
</ul>
li {
  list-style: none;
}

[data-pseude-content]::before {
  content: attr(data-pseude-content);
}

External CSS

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External JavaScript

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