Manual:$wgResourceLoaderLESSVars/en

Details
An associative array binding variable names to LESS code snippets representing their values. Removed in v1.31 due to concerns about allowing unmaintainable cross-dependencies. Custom  subclasses can override the   method instead.

Adding an item here is equivalent to writing  at the beginning of all your .less files, with all the consequences. In particular, string values must be escaped and quoted.

Changes to this configuration do NOT trigger cache invalidation.