I'm using a **mat-select** widget (of Angular-Material) in my app

I'm implementing a search bar **at the top of the select drowpdown** to filter options:

```
 <mat-select placeholder="Selectionner la boutique"
             id="libelleShop">
      <div id="custom-search-input" class="m-1 navbar-fixed-top">
         <input #shopKeyword matInput placeholder="Search"  class="search-input" (keyup)="filterShopsByLibelle(shopKeyword.value)">
       <span class="input-group-btn">
             <button class="btn btn-danger" type="button">
                <span class="glyphicon glyphicon-search"></span>
             </button>
       </span>
      </div>

      <mat-option *ngFor="let shop of bad3ShopsListSortedByName"
                          [value]="shop.edoId">
            {{shop.storeName}}
      </mat-option>
 </mat-select>

```

My purpose is how to keep the search Bard div (#custom-search-input) fixed on the top.

I've tried `position: fixed` but it seems to not work

**Suggestions ??**