postal/app/assets/stylesheets/application/components/_site_content.scss

.siteContent {
  align-items: stretch;
  display: flex;
  flex: 1 1 auto;
  overflow: hidden;
}

.siteContent__main {
  @include scrollbars(12px);
  flex: 1 1 auto;
  z-index:100;
  overflow-y:scroll;
  overflow-x:hidden;
}