MediaWiki:Multipms.css

.mp-ui-modal { position: absolute; left: 0; top: 0; background-color: rgba(0, 0, 0, 0.5); height: 100%; width: 100%; }

section#MP-ui-modal { background-color: white; padding: 8px; width: 650px; position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%); }