It turned out that the two cases where I couldn't apply a left margin or border were unrelated. Yesterday's was simply due to a typo in the style sheet (forgot the colon after margin-left). The sidebar one was a bit more involved, and it did indeed have to do with the content <div> being floated to the left. Despite it being floated, the links <div> on the right hand side still extended the full width of the browser window (as opposed to the 25% that it should have been allocated). Positioning it at an absolute of 75% from the left and making its width 25% fixed the problem.