If an absolutely positioned element has no parent with a position property, what will it be positioned relative to?

If an element with absolute positioning has no parent with an explicitly set position property (other than static), it will be positioned relative to the browser window (viewport). This is because the browser searches for the nearest ancestor with position: relative|absolute|fixed|sticky. If none is found, the reference point becomes the root element of the document, i.e., the viewport.

Example:

.parent {
  /* position: static by default */
}
.child {
  position: absolute;
  top: 10px;
  left: 10px;
}

In this case, .child will be positioned relative to the browser window.