Contact form 7 CSS disappeared after WP update to 3.5!

Eh! I was afraid of that. I came here first, before upgrading. The last time I upgraded, I noticed that class names changed slightly, and broke things. I’m assuming this is what happened to you. Are you familiar with the Firebug extension for Firefox? It is great for examining your site, and seeing what each contact form 7 element has class-name wise. Then you can re-target them in your css.