Having just seen your fiddle your issue is because you are using display:inline-block. This takes whitespace in your html into account. display:inline-block is notorious for being difficult and has dodgy browser support.
Option 1:
Try removing the white space in your html can sometimes sort the problem.
Option 2:
Using a different display property such as display:block will definitely sort the problem. Live example: http://jsfiddle.net/mM6AB/3/