Grid & Bootstrap

Hey! I was wondering when it is a good idea to switch from using Plain CSS, as it is recommended for the earlier projects, to CSS Grid or Bootstrap. I am currently working on Javascript Algorithms section and alongside I work on the responsive web design projects.

At what time do you suggest, I start using Grid or learn Bootstrap instead of resorting to Plain CSS?

grid and flex box are still plain css, they are thought in the certification about pure css, you can use them, and they help a lot with responsiveness

bootstrap is in the front end frameworks and libraries certification, you can use it on those projects if you want