MediaWiki:Common.js

/* Any JavaScript here will be loaded for all users on every page load. */
mw.loader.using('mediawiki.util').then(function() {
    if (mw.config.get('wgNamespaceNumber') == -1) { // Target only Special pages
        // Apply background color to the whole page
        document.body.style.backgroundColor = 'yellow';

        // Target and style the logo element
        var logo = document.querySelector('.mw-wiki-logo');
        if (logo) {
            logo.style.width = '135px';
            logo.style.height = '135px';
            logo.style.backgroundSize = 'contain';
            logo.style.backgroundPosition = 'center';
            logo.style.backgroundRepeat = 'no-repeat';
        }
    }
});