Slack — compact theme

userContent.css

@-moz-document domain(slack.com) {
  /**
   * A super-compact mode for Slack.
   * Activate it with the "dense" theme in your profile preferences.
   */

  /* Messages */
  .dense_theme .message {
    font-size:   0.9rem !important;
    line-height: 1.0rem !important;
    padding-top:    1px !important;
    padding-bottom: 1px !important;
  }
  .dense_theme .inline_attachement,
  .dense_theme .inline_attachment .inline_attachment_wrapper {
    padding-top:    0.2rem !important;
    padding-bottom: 0.2rem !important;
  }
  .dense_theme .inline_attachement,
  .dense_theme .inline_attachment    .attachment_service_name,
  .dense_theme .inline_attachment    .attachment_title,
  .dense_theme .inline_attachment    .attachment_contents,
  .dense_theme .file_comment         .timestamp,
  .dense_theme .file_reference       .file_details,
  .dense_theme .message.file_share   .file_details,
  .dense_theme .message.file_mention .file_details,
  .dense_theme .message.file_upload  .initial_comment,
  .dense_theme .message              .file_name {
    font-size: 0.8rem !important;
  }
  .dense_theme .file_details {
    line-height: 1.0rem !important;
  }
  .channels_list_holder .unread_highlight {
    line-height: 1.0rem !important;
  }
  .dense_theme .message.divider {
    border-top: none !important;
  }
  .dense_theme .msg_inline_holder {
    margin-bottom: 0.25rem !important;
  }
  .dense_theme span.emoji-inner {
    width:  80% !important;
    height: 80% !important;
  }

  /* Sidebar */
  .dense_theme .channels_list_holder .section_holder {
    margin: 1rem 0px !important;
  }
  .dense_theme .channels_list_holder ul li,
  .dense_theme .channels_list_holder ul li a {
    line-height: 1.2rem !important;
    height:      1.2rem !important;
  }

  /**
   * To make the sidebar less visible, you can also add this sidebar theme in
   * your own profile prefs:
   * #FFFFFF,#FFFFFF,#FFFFFF,#2288CC,#2288CC,#454449,#93CC93,#2288CC
   */
}