The size ratio between the two columns is going to vary depending on the size of the screen you view it on.
The right column has its width fixed, because you have in-line styles on the top 3 textareas fixing their width at 660px, so they will never be less than that size. This means that the left column re-sizes to take whatever space remains after the ~660px taken by the right column.
The narrower the screen, the smaller the left column gets.