자식요소 예제
const wrap = document.querySelector('#wrap');
const box2 = wrap.querySelector(".box2");
const children = wrap.children;
형제요소 예제
const wrap = document.querySelector('#wrap');
const children = wrap.children;
const box2 = wrap.querySelector(".box2");
const prevEl = box2.previousElementSibling
const nextEl = box2.nextElementSibling;
부모요소 예제
const a = box2.querySelector("a");
const parentEl = a.parentElement;
console.log(parentEl);