yii2-app-basic | Yii 2.0 Basic Application Template | Web Framework library

Most of widgets in default views of yii2 projects use yii\bootstrap\BootstrapAsset (bootstrap 3). Do not expect it magically toggle when you call yii\bootstrap4\BootstrapAsset.

Your step 2.3 is just adds bootstrap 4 to all other libraries you call by using widgets.

What you can do:

1) make sure you are calling yii\bootstrap4\ widgets and not calling yii\bootstrap\BootstrapAsset or any assets that depends on this class. Examples:

• use yii\bootstrap4\Html;
• use yii\bootstrap4\Modal;
• use yii\bootstrap4\Tabs;
• use yii\bootstrap4\ActiveForm;

2) Remember that bootstrap 4 have different classes than bootstrap 3. So if you will apply it to default views it highly likely will break because it does not have some classes from other version, or js acting differently.