I wouldn't prefix with the type, as you can infer this in the selector if you must
form#contact {
property: value;
}
The method you described is known as Hungarian notation, and isn't very popular.
For what you mention, you could place your injected HTML inside one div with one unique class/id, which has a sort of localised reset. Look up CSS selector specificty to ensure your rules will take affect and not other rules in the host page's CSS. See this answer to a similar question regarding styling an element within a parent page.
