rails-docstore/app/assets/stylesheets/application.scss

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
 * or any plugin's vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *
 *= require_tree .
 *= require_self
 */

#columns {
  display: flex;

  #main {
    padding: 1em;
    flex: 1;
  }

  #side {
    padding: 1em 2em;
  }
}

@media all and (max-width: 800px) {
  #columns {
    flex-direction: column-reverse;
  }
}