input-group-sm

bootstrap5.css

bootstrap5.css
.input-group-sm > .form-control:not(textarea),
.input-group-sm > .custom-select {
  height: calc(1.5em + 0.5rem + 2px);
}
bootstrap5.css
.input-group-sm > .form-control,
.input-group-sm > .custom-select,
.input-group-sm > .input-group-prepend > .input-group-text,
.input-group-sm > .input-group-append > .input-group-text,
.input-group-sm > .input-group-prepend > .btn,
.input-group-sm > .input-group-append > .btn {
  padding: 0.25rem 0.5rem;
  font-size: 0.875rem;
  line-height: 1.5;
  border-radius: 0.2rem;
}
bootstrap5.css
.input-group-lg > .custom-select,
.input-group-sm > .custom-select {
  padding-right: 1.75rem;
}

html bootstrap5 Sample

入力グループのサイズ調整/小： input-group-sm

Small 
  <!-- 小サイズの入力グループ -->
  <div class="input-group input-group-sm mb-3">
    <div class="input-group-prepend">
      <span class="input-group-text" id="inputGroup-sizing-sm">Small</span>
    </div>
    <input type="text" class="form-control" aria-label="Small" aria-describedby="inputGroup-sizing-sm">
  </div>