For the pages using the left navigation (the ones using the basebuildpage.html template), the item corresponding to the selected page should have the .active class applied. So for example, if I am in the recipes table, the "Recipes" element in the left navigation should have the .active class applied.
toaster/master:213fef6e87cbf60d773e28d31653e3c626d4058e
commit 056fbc47c76f5ff238fb01302f0dce457dabc08d
verified in master:3e528d3e4bc542ca2f654c54363c56af0fb9f61b