外枠：border

ボーダーを追加する：!important

border border-top border-right border-bottom border-left


  <!-- 全辺ボーダー -->
  <span class="border">border</span>
  <!-- 上ボーダー -->
  <span class="border-top">border-top</span>
  <span class="border-right">border-right</span>
  <span class="border-bottom">border-bottom</span>
  <span class="border-left">border-left</span>

ボーダー色を設定する：border-*

border-primary border-secondary border-success border-danger border-warning border-info border-light border-dark border-white


  <span class="border border-primary">border-primary</span>
  <span class="border border-secondary">border-secondary</span>
  <span class="border border-success">border-success</span>
  <span class="border border-danger">border-danger</span>
  <span class="border border-warning">border-warning</span>
  <span class="border border-info">border-info</span>
  <span class="border border-light">border-light</span>
  <span class="border border-dark">border-dark</span>
  <span class="border border-white">border-white</span>

ボーダーを削除する：border-0

border-0 border-top-0 border-right-0 border-bottom-0 border-left-0


  <!-- 全ボーダー削除 -->
  <span class="border border-0">border-0</span>
  <span class="border border-top-0">border-top-0</span>
  <span class="border border-right-0">border-right-0</span>
  <span class="border border-bottom-0">border-bottom-0</span>
  <span class="border border-left-0">border-left-0</span>