CSS

  .bootstrap-select {
    width: 300px !important;
   
  }
  /* .bootstrap-select::after {
    content: none;
  }
     */
    
  .btn-custom {
    color: black;
    /* background-color: blue; */
    border-color: red;
    border-radius: 10px;
  }
  .btn-custom::after {
    content: url(/extras/drop.png);
    /* width: 95%; */
  }
  .btn-custom::before {
    content: none;
  }
 .bootstrap-select > .dropdown-toggle.bs-placeholder.btn-custom,
  .bootstrap-select > .dropdown-toggle.bs-placeholder.btn-custom:hover,
  .bootstrap-select > .dropdown-toggle.bs-placeholder.btn-custom:focus,
  .bootstrap-select > .dropdown-toggle.bs-placeholder.btn-custom:active {
    color: black;
  }

HTML enter code here

<select class="selectpicker" data-style="btn-custom" multiple data-max-options="4" data-actions-box="true">
                        <option>Mustard</option>
                        <option>Ketchup</option>
                        <option>Relish</option>
                        <option>Relish</option>
                        <option>Relish</option>
                        <option>Relish</option>
                        <option>Relish</option>
                      </select>

Bootstrap Cdn version 4.1.1 my select feild I want to use my image instead of the arrow on the field and want to remove the default icon or any other way I can use it??