Bootstrap添加相邻div之间似乎是两个像素边距的内容

I have a question that I believe pertains to the Bootstrap framework. Whenever I import bootstrap it looks like it makes two adjacent divs have a 2 pixel margin between them, although nothing in the element inspector suggests what could be causing this. Removing the very first line in the linked fiddle makes the spacing go away. Would anybody be able to tell me what causes this spacing? Again, I cannot seem to figure out what is causing this from using the element inspector. I'm basically looking at the spacing between the red and the green divs. I appreciate you taking the time to help me.I have a question that I believe pertains to th