[Plugin: Contact Form 7] Adding class to form

wpcf7_form_class_attr filter is available. Add this code to your theme’s functions.php.

add_filter( 'wpcf7_form_class_attr', 'your_custom_form_class_attr' );

function your_custom_form_class_attr( $class ) {
	$class .= ' foo bar';
	return $class;
}

Takayuki Thanx, it works ??
But what about if I need also to add a class to the button?

For each field in a form, you can add ‘class:’ option in the tag.

Example:
[text* your-name 20/40 class:required "John Smith"]

See docs.
Text Fields

what code do I add to this to move the box to the right?

`[select your-country class:class-name1 “Australia” “Brazil” “Canada” “Denmark” “Finland”]

Thanks

.class-name1 {
float:right;
}