bootstrap4.css
.pre-scrollable {
  max-height: 340px;
  overflow-y: scroll;
}
bootstrap4.css
@media (max-width: 575.98px) {
  .table-responsive-sm {
    display: block;
    width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
  .table-responsive-sm > .table-bordered {
    border: 0;
  }
}
bootstrap4.css
@media (max-width: 767.98px) {
  .table-responsive-md {
    display: block;
    width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
  .table-responsive-md > .table-bordered {
    border: 0;
  }
}
bootstrap4.css
@media (max-width: 991.98px) {
  .table-responsive-lg {
    display: block;
    width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
  .table-responsive-lg > .table-bordered {
    border: 0;
  }
}
bootstrap4.css
@media (max-width: 1199.98px) {
  .table-responsive-xl {
    display: block;
    width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
  .table-responsive-xl > .table-bordered {
    border: 0;
  }
}
bootstrap4.css
.table-responsive {
  display: block;
  width: 100%;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
bootstrap4.css
.modal-dialog-scrollable {
  display: -ms-flexbox;
  display: flex;
  max-height: calc(100% - 1rem);
}
bootstrap4.css
.modal-dialog-scrollable .modal-content {
  max-height: calc(100vh - 1rem);
  overflow: hidden;
}
bootstrap4.css
.modal-dialog-scrollable .modal-header,
.modal-dialog-scrollable .modal-footer {
  -ms-flex-negative: 0;
  flex-shrink: 0;
}
bootstrap4.css
.modal-dialog-scrollable .modal-body {
  overflow-y: auto;
}
bootstrap4.css
.modal-dialog-centered.modal-dialog-scrollable {
  -ms-flex-direction: column;
  flex-direction: column;
  -ms-flex-pack: center;
  justify-content: center;
  height: 100%;
}
bootstrap4.css
.modal-dialog-centered.modal-dialog-scrollable .modal-content {
  max-height: none;
}
bootstrap4.css
.modal-dialog-centered.modal-dialog-scrollable::before {
  content: none;
}
bootstrap4.css
.modal-scrollbar-measure {
  position: absolute;
  top: -9999px;
  width: 50px;
  height: 50px;
  overflow: scroll;
}
bootstrap4.css
@media (min-width: 576px) {
  .modal-dialog {
    max-width: 500px;
    margin: 1.75rem auto;
  }
  .modal-dialog-scrollable {
    max-height: calc(100% - 3.5rem);
  }
  .modal-dialog-scrollable .modal-content {
    max-height: calc(100vh - 3.5rem);
  }
  .modal-dialog-centered {
    min-height: calc(100% - 3.5rem);
  }
  .modal-dialog-centered::before {
    height: calc(100vh - 3.5rem);
  }
  .modal-sm {
    max-width: 300px;
  }
}
■ドロップダウン:dropdown-menu:コンポーネント:ドロップダウンメニューのオーバーフローを制約する境界を設定する

  <div class="bg-info text-center" style="width:250px;height:250px;overflow:scroll;">
    <br><br><br>
    <div class="dropdown">
      <button class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" data-boundary="scrollParent">ドロップダウンボタン</button>
      <div class="dropdown-menu">
        <a href="#" class="dropdown-item">スクロールウィンドウ幅で制約されるドロップダウンメニュー</a>
        <a href="#" class="dropdown-item">スクロールウィンドウ幅で制約されるドロップダウンメニュー</a>
        <a href="#" class="dropdown-item">スクロールウィンドウ幅で制約されるドロップダウンメニュー</a>
      </div>
    </div>
  </div>