The EU executive body is the Commission itself. When it comes to technical details, what happens depends on the actual legislation. There are plenty of technic

The EU executive body is the Commission itself. When it comes to technical details, what happens depends on the actual legislation. There are plenty of technical committees in Bruxelles (in fact, some would say there are too many of those...), but for situations where some trickery in application or enforcement is expected, directives stay light on details and national governments will then get a good degree of freedom in adapting the rules. If a government implements a directive badly, it will eventually be challenged in the European Court of Justice, that will decide if the national rules follow the spirit of the directive.