Contact form 7 breaks when using JP Custom CSS. This is the fix.

class.jetpack,php

<?php

class Jetpack {
	/**
	 * Get $content_width, but with a <s>twist</s> filter.
	 */
	public static function get_content_width() {
		$content_width = isset( $GLOBALS['content_width'] ) ? $GLOBALS['content_width'] : false;
		return apply_filters( 'jetpack_content_width', $content_width );
	}

        /**
         * Prevents other plugins breaking when testing the jetpack class
         */
        public static function __callStatic($name, $arguments) { 
          return false;
        }
}