we don’t use any frameworks, the limited CSS that the theme uses for its layouts is Flexbox CSS that is generated dynamically. So there are no classes for content. We moved away from this as Block Editing is the main driver and we created GenerateBlocks for that very kind of thing.
If you’re not a block editor user then you can implement your own CSS framework for content. I would personally avoid Bootstrap unless you need the large amount of code it creates and can handle that some its classes eg. container may conflict with the theme or other plugins.