gitlab-org--gitlab-foss/app/assets/stylesheets/sections/issuable.scss

@media (max-width: $screen-sm-max) {
  .issuable-affix {
    margin-top: 20px;
  }
}

@media (max-width: $screen-md-max) {
  .issuable-affix {
    position: static;
  }
}

@media (min-width: $screen-md-max) {
  .issuable-affix {
    &.affix-top {
      position: static;
    }

    &.affix {
      position: fixed;
      top: 70px;
      width: 220px;
    }
  }
}