Single post in Guide to CSS: Beginner to Expert

Hello! I only recently starting playing around with CSS and I've been working on making myself a signature. I'm sure there's plenty of mistakes, but I'm fairly pleased with how it turned out. However, there's one issue I cann't seem to resolve: there's a border underneath the flower tabs that just won't go away. I have all borders and backgrounds set as 'none'. On my screen, the border is green (because of my site skin??). I'm really at a loss on why it's here and what to do about it. Any help would be appreciated!