When you select a date, the date correctly enters the input field. However, the calendar itself, despite the fact that the date has already been selected, does not disappear. 
Here is the code:
<?= $form->field($model, 'date_complete')->widget(DatePicker::classname([ 'options' => [ 'style' => 'width: 40%;', ], 'pluginOptions' => [ 'language' => 'ru', 'todayHighlight' => true, 'format' => 'dmy', 'type' => DatePicker::TYPE_BUTTON, ], ] )); ?>