Adding HTML and CSS stylesheets to posts

Hi,
I’m trying to add HTML to a single post and then have unique CSS for just that page. I installed a plugin called specific CSS that allows you to link CSS for just that page.

Here is the page I am working on..

http://www.elementary-agency.com/marketing-hotels-packages/

As you can see it has now aligned the page slightly differently then the other pages:

http://www.elementary-agency.com/

Can anyone let me know if this is the best way to create a unique page or any css that i can adjust for that page.

Thanks for your help in advance.

Nick