MediaWiki:Common.js

/* Any JavaScript here will be loaded for all users on every page load. */
mw.loader.using('mediawiki.util', function () {
    if (mw.config.get('wgCanonicalSpecialPageName') === 'Preferences') {
        var css = `
            .mw-htmlform-field-HTMLTextField {
                background: #fef6e0;
            }
        `;
        var style = document.createElement('style');
        style.innerHTML = css;
        document.head.appendChild(style);
    }
});