Template:MainPageWelcomeCSS.css

.wiki-banner-wrapper {
  border: 2px solid #f79200;
  width: 100%;
  max-width: 100%;
  margin: 0 auto;
  overflow: hidden;
  padding: 0;
  box-sizing: border-box;
}

.wiki-banner-image img {
  width: 100%;
  height: auto;
  display: block;
}