Can't use CSS in Post for image?

Hello everyone,

I can'nt save my css (border and background) for image in this Post?
I have a short code css for image in this post, but when I refesh Post.... it haven'nt effect???

Who can help me this problem?
This is my post: http://newsky.edu.vn/luyen-thi-toeic-cap-toc-450/

Thanks all