Theming

Theming is done with Bootstrap 5 CSS and usually it is not needed to do anything. The input field class should have at minimum the class form-control in order to use the Boostrap 5 styling. Any other classes can be used for this field like this

<div class="row mb-3 g-3">
    <div class="col-md-4">
        <label for="customer" class="form-label">Customer</label>         
        <input id="customer" name="customer" size="30" type="text" class="form-control autocomplete" placeholder="Type Customer Name"/>
    </div>
</div>

The autocomplete list which appear when typing can be styled with option activeClasses. This option is array where the first element is the bootstrap 5 backgroung and the second is the text color. By default this option is set like this

$autcomplete_defaults = array(
...
    "activeClasses" => array("bg-primary", "text-white"),
...
);

To set black background when highlight and blue test use this

$ac->setOption("activeClasses", array("bg-dark", "text-primary"));