Twenty Twelve Theme & Post Format Styles

I’m not sure if this is the right place, but hopefully you can help. I’m using the Twenty Twelve theme on my blog. I’ve modified the background and the colours, but that’s all. I noticed that most of the styling for post formats in the theme don’t match what is displayed in the demo version of the blog. Can anyone think why this might be the case?

I’ve deleted almost all of my other themes from the server just to make sure there’s no CSS cascading issues that might be getting in the way, but beyond that, I’m stumped. Thanks in advance for the help.