discourse/app/assets/stylesheets/mobile/banner.scss

// --------------------------------------------------
// Banner
// --------------------------------------------------

#banner {
  // go full width on mobile, by extending into the 10px wrap
  // borders on left and right
  margin: 0 -10px;

  @media all and (max-height: 499px) {
    max-height: 100px;
  }

  @media all and (min-height: 500px) {
    max-height: 180px;
  }

}