How to customize validation error message to display on tooltip in Yii2?

Yii 2.0
1

I am using ActiveForm of yii2 and I want to customize the validation errors. I want to display errors on tooltip.

This is my form

<?= $form = ActiveForm::begin(['id' => 'login-form','method'=>'post']); ?> 
<?= 
    $form->field($model, 'email')
        ->textInput([
            'class'=>'form-control login_email',
            'placeholder'=>'Email'
            /*'onfocus'=>"this.value = '';",
            "onblur"=>"if (this.value == '') {
                this.value = 'Email';
            }"*/
        ])
        ->label(false);
?>
<?= 
    $form->field($model, 'password')
        ->passwordInput([
            'class'=>'form-control',
            'placeholder'=>'Password'
        ])
        ->label(false);
?>
<input type="text" name="hidden" value="login" hidden="true">
<p class="forgot">
    <a href="<?= Yii::$app->urlManager->createUrl(['site/request-password-reset']); ?>">
        Forgot Password?
    </a>
</p>

<div class="form-group">
    <?= Html::submitButton('Log In', ['class' => 'sign-in','name' => 'login-button']) ?>
</div>
<?php ActiveForm::end(); ?>

Please tell me if anyone has idea about this.