Overheads on a boat are typically low and have minimal depth behind the headlining. Marine downlights are specifically design for this. Most modern marine downlights are now LED which has resulted in the form of the fixtures becoming more compact and smaller.
Recessed light fixtures are the most common lighting found on boats and careful positioning means they can be used as main area lighting and also soft ambience. Not all LED lights are dimmable so make sure you plan ahead before install.
Older style downlights typically were halogen or incandescent and although these fixtures are still available to buy they tend to be for additions to existing vessels.