HTML CSS the opposite to display:none
A true opposite to display: none there is not (yet).
But display: unset is very close and works in most cases.
From MDN (Mozilla Developer Network):
The unset CSS keyword is the combination of the initial and inherit keywords. Like these two other CSS-wide keywords, it can be applied to any CSS property, including the CSS shorthand all. This keyword resets the property to its inherited value if it inherits from its parent or to its initial value if not. In other words, it behaves like the inherit keyword in the first case and like the initial keyword in the second case.