debian-mirror-gitlab/app/assets/stylesheets/framework/system_messages.scss

.header-message,
.footer-message {
  padding: 0 15px;
  border: 1px solid transparent;
  border-radius: 0;
  position: fixed;
  left: 0;
  width: 100%;
  text-align: center;
  margin: 0;
  z-index: 1000;

  p {
    @include str-truncated(100%);
    margin-top: -1px;
    margin-bottom: 0;
    font-size: $gl-font-size-small;
  }
}

.header-message {
  top: 0;
  height: $system-header-height;
  line-height: $system-header-height;
}

.footer-message {
  bottom: 0;
  height: $system-footer-height;
  line-height: $system-footer-height;
}

.with-performance-bar {
  .header-message {
    top: $performance-bar-height;
  }
}

// System Header
.with-system-header {
  // main navigation
  // login page
  .navbar-gitlab,
  .fixed-top {
    top: $system-header-height;
  }

  // left sidebar eg: project page
  // right sidebar eg: MR page
  .nav-sidebar,
  .right-sidebar {
    top: $system-header-height + $header-height;
  }

  .content-wrapper {
    margin-top: $system-header-height + $header-height;
  }

  // Performance Bar
  // System Header
  &.with-performance-bar {
    // main navigation
    header.navbar-gitlab {
      top: $performance-bar-height + $system-header-height;
    }

    .layout-page {
      margin-top: $header-height + $performance-bar-height + $system-header-height;
    }

    // left sidebar eg: project page
    // right sidebar eg: MR page
    .nav-sidebar,
    .right-sidebar {
      top: $header-height + $performance-bar-height + $system-header-height;
    }
  }
}

// System Footer
.with-system-footer {
  // left sidebar eg: project page
  // right sidebar eg: mr page
  .nav-sidebar,
  .right-sidebar,
  // navless pages' footer eg: login page
  // navless pages' footer border eg: login page
  &.devise-layout-html body .footer-container,
  &.devise-layout-html body hr.footer-fixed {
    bottom: $system-footer-height;
  }

  .content-wrapper {
    margin-bottom: 16px;
  }

  .boards-list {
    height: calc(100vh - #{$header-height + $breadcrumb-min-height + $performance-bar-height + $system-footer-height + $gl-padding-32});
  }
}

.fullscreen-layout {
  .header-message,
  .footer-message {
    position: static;
    top: auto;
    bottom: auto;
  }
}