CSS GRid Rows and Columns that should not be there.(Bugs?)

I came to PG mainly for CSS Grid. There is one thing I have noticed that confuses me.

  1. How can I reset the Grid? If I trash the grid while experimenting, I do not expect it to retain the CSS that I previously associated an element. If I try and create a new grid, I would expect it to be fresh and the elements to not be assigned to any part of the grid. As of now, the CSS from an experiment that I want to forget is still there.

  2. Does the css code for the grid go on the style.css?

  3. Even after I trashed one grid experiment (which had many colums and rows), when I bring the grid back, it is not correct. This is what I am seeing.

Are these known bugs?