Centering-a-div Memes

Someone who can center a div both vertically AND horizontally without Googling it is basically a mythical creature. Frontend devs have been battling this since the dawn of CSS, cycling through margin auto, flexbox, grid, absolute positioning with transforms, and probably a blood sacrifice or two. The fact that it requires clarification of both axes just adds insult to injury. Flexbox finally made this trivial, but the trauma runs deep. We all still whisper about the dark days of table layouts and vertical-align: middle that never worked.