[css] Is there an opposite to display:none?

You can use display: block

Example :

<!DOCTYPE html>
<html>
<body>

<p id="demo">Lorem Ipsum</p>

<button type="button" 
onclick="document.getElementById('demo').style.display='none'">Click Me!</button>
<button type="button" 
onclick="document.getElementById('demo').style.display='block'">Click Me!</button>

</body>
</html>