discourse/app/assets/stylesheets/common/printer-friendly.scss

@media print {
  /* remove items N/A for print
  ** visual clutter etc. */
  .avatar,
  .topic-avatar,
  header,
  .topic-above-post-stream-outlet.topic-above-post-stream,
  .topic-map,
  .post-menu-area.clearfix,
  div#topic-footer-buttons,
  div.suggested-topics,
  div#progress-topic-wrapper,
  #topic-progress-wrapper,
  div.nums,
  ._flyout,
  #topic-progress,
  .quote-controls,
  .topic-timer-info,
  div.lazy-video-container,
  .post-info.edits,
  .post-action,
  .saving-text,
  .draft-text,
  .discourse-modal,
  div.read-state,
  div.read-state.read,
  .edit-topic,
  a.reply-to-tab,
  a.reply-new,
  div.time-gap,
  #bottom,
  #footer,
  .alert-info,
  .badge-category,
  .badge-category-bg,
  .badge-notification.clicks,
  .crawler-nav,
  .powered-by-link,
  .timeline-container,
  .poll-info {
    display: none !important;
  }
  /* For readability */
  a,
  a:visited {
    color: #0088cc !important;
  }
  /* bottom border to help separate posts */
  div.row {
    border-top: 1px solid #aaa;
  }
  .cooked pre code {
    max-height: none;
  }
  #main-outlet {
    padding: 0 !important;
  }
  html,
  body {
    min-width: 0;
    height: auto;
  }
  .lightbox-wrapper img {
    max-width: 500px !important;
    height: auto !important;
  }
  .topic-body {
    width: auto;
    margin: 0;
    padding: 0;
    float: none;
  }
  .topic-post article.boxed .select-posts {
    width: auto;
    left: auto;
    right: 0;
  }
  .gap {
    width: auto;
  }
  /* restyle div#topic-title */
  #topic-title {
    margin: 0;
    padding: 0;
  }
  #topic-title div div h1 {
    margin: 2.5em 0 0 0;
    padding: 0;
    float: left;
    font-weight: normal;
    font-size: normal;
  }
  a,
  a:visited {
    color: #ddd;
    font-weight: bold;
  }
  /* localhost  - MOOT for production */
  .topic-category-outlet.show-topic-category-location,
  div.alert.alert-info.alert-emails-disabled,
  div.profiler-results.profiler-left.profiler-no-controls {
    display: none;
  }
}