The MediaWiki Code editor knows no CSS variables and shows errors/Warnings.

• https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties
• https://www.w3schools.com/css/css3_variables.asp

Example:

{
  --media-rollback: #B40404;
...
...

.mw-rollback-link a  {
   color: var(--media-rollback);
}

Error: Expected RBRACE at line 2, col 3.

and

Warning: Expected (<color> | inherit) but found 'var(--global-rollback)'.