Those frameworks I mentioned are built into Site Designer, and they have had quite an upgrade since 2019. I see from the file you posted that you are using Frameworkless desktop-down.
When opening SD you get to a screen showing you a list of templates to the left. If you choose 'Blank', you will see the different frameworks/layout systems you can choose among in SD. If you then just cancel that screen, the program will open Frameworkless desktop down as the default with a standard 'startup-template. If you used that, or parts of that, to start your design, I can understand why you all of a sudden got the CSS grid system mixed in.
To avoid any premade template (if that is what you want), you need to select one of the ones available under 'Blank' on that first screen. Even if you select Frameworkless desktop down, it will come up empty, without the startup thingie.
That is interesting, I will look at that.
It has been a few years since I built a website, it was a little easier with the earlier versions Site Designer.
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