The Ultimate HTML5 & CSS3 Series: Part 1 Borders

In the Borders video, when he types in border-width: 10px 20px 10px 20px; why is his right border narrower than his left? Mine are equal and that seems how they should be according to those numbers but when he shows his results at 2:34 in the video his right border is narrower than his left. Why and what is happening?

Hi, its just that his recording window is slightly cut off on the right, but those borders should be equal width