message: chore(dropdown-item): add shadow parts
diff: @@ -18,6 +18,7 @@ const { prefix } = settings;
  /**
  * Dropdown item.
  * @element bx-dropdown-item
  + * @csspart selected-icon The selected icon.
  */
  @customElement(`${prefix}-dropdown-item`)
  class BXDropdownItem extends LitElement {
  @@ -59,7 +60,7 @@ class BXDropdownItem extends LitElement {
  return html`
  <div class="${prefix}--list-box__menu-item__option">
  <slot></slot>
  - ${!selected ? undefined : Checkmark16({ class: `${prefix}--list-box__menu-item__selected-icon` })}
  + ${!selected ? undefined : Checkmark16({ part: 'selected-icon', class: `${prefix}--list-box__menu-item__selected-icon` })}
  </div>
  `;
  }
  