The reason this number is changed is for a somewhat tricky reason.  The right column is supposed to be 250px, which is what you had.  However, the way css renders the divs is a little weird.  They may have mentioned it in class, but it has to do with what they call the CSS box model.

![box 1](https://f.cloud.github.com/assets/1758049/2181606/dac9da0a-9759-11e3-8afd-066a2a957869.png)

Basically, the padding you set is added to the width of the element.  You can see this if you're in chrome by inspecting the element (right click and select "inspect element").  In the source code, hover over the dl element and it'll show you what the actual dimensions are.  Since your padding is 10px, that means ten pixels are added to both sides, making it 270px wide instead of 250px. Dropping the width to 230px fixes it as 230+10+10 = 250