Each column also has a setting button. By clicking on it, you will see the following dialog box:
Here you can see the following fields:
- Extra Small Width
- Small Width
- Medium Width
- Medium Width
- Extra Large Width
All of these actually determine the bootstrap grid classes. For example, if the medium width is 8, it means that a class will be created like col-md-8. Similarly if you set grid columns for Extra Large or others, then their classes will also be created. Such as: col-md-8 col-xl-4 etc.
To understand bootstrap grid layout, please study bootstrap 4.
https://getbootstrap.com/docs/4.4/layout/overview/
Additionally the CSS class and custom style fields can be used in the same way as in row settings or widget settings.