help with blogger

So you might have noticed recently I keep having highlighted sections in my post.  This is not intentional.  Tends to happen if I past something in but not even sure why it happened in the last one where I didn't think I did.  I have played around and can't figure out how to make it not look so choppy.  If anyone out there has blogger experience and a suggestion, I would be grateful to know.  Sorry to readers when if harder to read.  I am trying to fix!