You’re right that position: absolute works similarly to CSS, and the top, left, right, and bottom values are all between 0 and 1 (so 5% would be 0.05). When you’re pinning something to the right, don’t use left; use right: 0.05, and that’ll anchor it 5% away from the right edge. If you mix left and right, it’ll stretch the element between them, which might not be what you’re going for.
The system assumes the pivot is top-left, so to truly center something, set top: 0.5, left: 0.5, and use transform: translate(-50%, -50%) to offset it back by half its size. That gives you a centered pivot visually, even though the actual pivot hasn’t changed.
This MDN article might help as a refresher, since positioning here really does follow standard CSS behavior. And there’s also a good breakdown on anchoring in this thread: Setting an Anchor Point - #2 by GeorgeButler