border-right

bootstrap5.css

.dropdown-toggle::after {
  display: inline-block;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid;
  border-right: 0.3em solid transparent;
  border-bottom: 0;
  border-left: 0.3em solid transparent;
}

bootstrap5.css

.dropup .dropdown-toggle::after {
  display: inline-block;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0;
  border-right: 0.3em solid transparent;
  border-bottom: 0.3em solid;
  border-left: 0.3em solid transparent;
}

bootstrap5.css

.dropright .dropdown-toggle::after {
  display: inline-block;
  margin-left: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid transparent;
  border-right: 0;
  border-bottom: 0.3em solid transparent;
  border-left: 0.3em solid;
}

bootstrap5.css

.dropleft .dropdown-toggle::before {
  display: inline-block;
  margin-right: 0.255em;
  vertical-align: 0.255em;
  content: "";
  border-top: 0.3em solid transparent;
  border-right: 0.3em solid;
  border-bottom: 0.3em solid transparent;
}

bootstrap5.css

.list-group-flush .list-group-item {
  border-right: 0;
  border-left: 0;
  border-radius: 0;
}

bootstrap5.css

.bs-tooltip-right .arrow::before,
.bs-tooltip-auto[x-placement^="right"] .arrow::before {
  right: 0;
  border-width: 0.4rem 0.4rem 0.4rem 0;
  border-right-color: #000;
}

bootstrap5.css

.bs-popover-right > .arrow::before,
.bs-popover-auto[x-placement^="right"] > .arrow::before {
  left: 0;
  border-width: 0.5rem 0.5rem 0.5rem 0;
  border-right-color: rgba(0, 0, 0, 0.25);
}

bootstrap5.css

.bs-popover-right > .arrow::after,
.bs-popover-auto[x-placement^="right"] > .arrow::after {
  left: 1px;
  border-width: 0.5rem 0.5rem 0.5rem 0;
  border-right-color: #fff;
}

bootstrap5.css

.spinner-border {
  display: inline-block;
  width: 2rem;
  height: 2rem;
  vertical-align: text-bottom;
  border: 0.25em solid currentColor;
  border-right-color: transparent;
  border-radius: 50%;
  -webkit-animation: spinner-border 0.75s linear infinite;
  animation: spinner-border 0.75s linear infinite;
}

bootstrap5.css

.border-right {
  border-right: 1px solid #dee2e6 !important;
}

bootstrap5.css

.border-right-0 {
  border-right: 0 !important;
}

html bootstrap5 Sample

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>