bootstrap-select
Позволяет использовать стилизованные выпадающие списки. Плагин мультиязычный, поэтому установите язык в своем приложении., (*1)
Installation
The preferred way to install this extension through composer., (*2)
You can set the console, (*3)
$ composer require "scorpsan/bootstrap-select"
or add, (*4)
"scorpsan/bootstrap-select": "*"
in require section in composer.json file., (*5)
Using
Once the extension is installed, simply use it in your code by  :, (*6)
Add following code to your configuration file of application:, (*7)
field($model, 'id')->dropDownList($items, [
    'class'  => 'form-control selectpicker',
    'data' => [
        'style' => 'btn-success',
        'live-search' => false,
        'size' => 7,
        'title' => 'Choose one...'
    ]]);
echo $form->field($model, 'id')->dropDownList($items, [
    'class'  => 'form-control selectpicker',
    'data' => [
        'style' => 'btn-primary',
        'live-search' => true,
        'size' => 7,
        'title' => 'Choose one...',
    ],
]);
echo $form->field($model, 'id')->dropDownList($items, [
    'class'  => 'form-control selectpicker',
    'multiple' => true,
    'data' => [
        'style' => 'btn-warning',
        'live-search' => false,
        'size' => 7,
    ],
]);
echo Html::dropDownList('item', null, $items, [
    'class'  => 'form-control selectpicker',
    'data' => [
        'style' => 'btn-info',
        'live-search' => false,
        'size' => 7,
        'title' => 'Choose one...',
    ]
]);
echo Html::dropDownList('item', null, $items, [
    'class'  => 'form-control selectpicker',
    'data' => [
        'style' => 'btn-default',
        'live-search' => true,
        'size' => 7,
        'title' => 'Choose one...',
    ]
]);
...
?>