Please note that the guide that you are looking at is not for SD3 it is for CSS Grid which are two completely different apps. If you are working in SD3 it is important that you start in fallback first then move to the Grid otherwise your styles will have to be completely redone when switching from grid to fallback.
If you do it the other way around your stylings will carry forward to the grid.
Here are some tutorials that are very useful
https://www.youtube.com/channel/UCpm5RQ … amp;view=1
Hope this helps
https://www.youtube.com/channel/UCL8qVv … ttneYaMSJA