Setting % widths for responsive design
When setting % widths for div class elements "within" a container, do you set the % with respect to the width of the container, or to the width of the entire viewable width of the page?
For example, let's say you had a container set at 70% width with respect to the entire viewable and scalable page width. Within this container, I want 2 equally sized columns that split the width of the container 50/50.
Would I set my interior element widths to 50% (half of the container width), or 35% (half of the container width with respect to the entire 100% full page width)?