How would magic work if it was a science?

Magic used to be a science of the arcane. The ancient civilizations of the world were so skilled in the science of magic that they could use it to push back the darkness and create safe zones for humanity. After their fall, magic was twisted and became a relic of a bygone era. Not only is magic studied by mages, but it is also studied by scientists. What are the rules of magic? Not only as a fantasy element but as a science? <br><br>Edit: Holy cow this blew up