How do I style an “auto-complete-select”-Dropdown-List like an “abp-select”-Dropdown-List

I build a create-form for my application and used the tag-helpers

abp-select asp-for="MyModelField" 

(normal Dropdown-List with static option-values from Enum)
and

<select asp-for="MyOtherModelField"
        class="auto-complete-select"
        data-autocomplete-api-url="/api/app/lookup/my-function-name"
        data-autocomplete-display-property="name"
        data-autocomplete-value-property="id"
        data-autocomplete-items-property="items"
        data-autocomplete-filter-param-name="filter"
        data-autocomplete-allow-clear="true">
</select>  

(auto-complete List with values calculated with ajax-request)

The result of these two lines is this: the two different Dropdown-Lists

I now want the second Dropdown-List to look like the first.
Can anybody tell me some keywords to google for or maybe a short tutorial how to “copy the style”?

I tried to inspect the classes of the first Dropdown-List with the developer-tools in Chrome and add different classes to the autocomplete-select-tag (for example the class “form-select”). But nothing changed.