function calcDistanceBetweenCenters(elA, elB) {
    const centerOfA = findCenterOfElement(elA);
    const centerOfB = findCenterOfElement(elB);
    return calcDistance(centerOfA, centerOfB);
}
@param {HTMLElement|ChildNode} elA
@param {HTMLElement|ChildNode} elB
@return {number}