No matter what you are using, they are always there, editable/hackable.
However I would argue that it makes it slightly harder to make any change. You no longer have a single class with all the styles that are affecting that element.
You can change the classes in the harder to read html, or override the single element.
There is no longer the possibility to, for example, affect all .primary-btns.
Everyone's experience differs quite a bit depending on the used client library (plain, apollo or relay) or the server library specific for your server languages.
However I would argue that it makes it slightly harder to make any change. You no longer have a single class with all the styles that are affecting that element.
You can change the classes in the harder to read html, or override the single element. There is no longer the possibility to, for example, affect all .primary-btns.