Manual:$wgLogoHD

Details
Array with URL paths to HD versions of the wiki logo.

The scaled logo size should be under 135x135 pixels, the same as .

Only 1.5x and 2x versions are supported.

Example:

Older MediaWiki versions
If you're using MediaWiki versions older than 1.25, you can add the following snippet to your MediaWiki:Common.css: