querySelector.

querySelector(selector) returns the first matching element or null. Selectors look like CSS: #id, .class, tag.

Store the result in a variable, then read or write properties. If the element is missing, access throws — check carefully in later lessons.

Mini example:

const title = document.querySelector("#title"); title.textContent = "Budget";

Common mistake: querySelectorAll (a list) instead of querySelector; or a selector without # for an id.