The default template (bootstrap4), located at /resources/simple-crud/stubs/views/, is used to generate views and fields.
In order to use your custom template, create a folder at /resources/simple-crud/stubs/views/ with a name eg. mytemplate and create all the required stubs that are stored in the default bootstrap4 directory.
It is recommended that you copy all the files from bootstrap4 directory into your new template directory and then modify the files according to your need.
To generate views using your template, use the --template option of the View command as follows:
php artisan crud:view Post --fields='title:string; body:text; author:string;' --template=mytemplate
So, now the views will be generated as per the mytemplate template.