Give the parent a perspective (how strong the 3D depth feels) and the rotating element transform-style: preserve-3d. Stack the front and back faces on top of each other, pre-rotate the back rotateY(180deg), and set backface-visibility: hidden on both so the face pointing away never shows through.
A smaller perspective value (say 400px) exaggerates the depth distortion for a more "close to camera" feel; a larger one (1200px+) reads as flatter, more subtle rotation.
When to use
Use it when the front and back genuinely hold different content (a question/answer, a summary/detail). For just switching screens, a fade or slide reads better.