Use 25/75 split on sections with narrow first column (usually a heading) followed by large content area that isn't split into smaller columns.
On medium screens the 25/75 split is adjusted to be 33/66 (2 columns and 4 columns)
On small screens it becomes 2 rows of 100 + 100 split.
To achieve that use row--25-75 class name on the row and col on the columns.