Green is column at site width. Container border l/r is 5px, column border is 10px.

blue is column 50% width. Container border l/r is 10px

blue is column 50% width. Container border l/r is 10px

orange is column 33% width

orange is column 33% width

orange is column 33% width

green is column 2/3 width. 0 column spacing left and right.

orange is column 1/3 width

orange is column 1/3 width

green is column 2/3 width