Which one is better to use, a CSS grid or a Bootstrap, for a layout?

[ArielLeslie]

CSS3 Grids vs. Bootstrap

So I started FCC and Codeacademy like 2 or 3 years ago and at the point we learned a bit of HTML and CSS and then went on to learn Bootstrap. Which we were told was used by a crazy amount of legit websites. So now, FCC is teaching more of the CSS3 and the grid structure which seems exactly like Boostraps basic layout. My question is why? Is the grid structure in CSS3 new? Is it better to use the grid in CSS3 than Bootstrap? Thanks in advance! -Naomi