rounded-bottom

bootstrap5.css

.rounded-bottom {
  border-bottom-right-radius: 0.25rem !important;
  border-bottom-left-radius: 0.25rem !important;
}

html bootstrap5 Sample

角丸：rounded

rounded rounded-top rounded-right rounded-bottom rounded-left rounded-circle rounded-0

  <!-- 背景色を設定しない限り適用されない、背景に適用される -->
  <span class="rounded bg-warning">rounded</span>
  <span class="rounded-top bg-warning">rounded-top</span>
  <span class="rounded-right bg-warning">rounded-right</span>
  <span class="rounded-bottom bg-warning">rounded-bottom</span>
  <span class="rounded-left bg-warning">rounded-left</span>
  <!-- サークル -->
  <span class="rounded-circle bg-warning">rounded-circle</span>
  <span class="rounded-0 bg-warning">rounded-0</span>