margin: 0 0 40px;
As far as I know, you can specify 1, 2 or 4 values for margin, but not 3.
And are you sure you want to use "px" and "in" as units? Pixels are very device-specific, two screens with the same size but with different resolution will have different margins. Inches are quite absolute, no matter how big or small the screen and the font, they stay the same. You might consider using percent lengths or "em".