Mozilla DeveloperDocument: querySelector() method The Document method querySelector() returns the first Element within the document that matches the specified CSS selector, or group of CSS selectors. If no matches 更多内容请查看https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelector
W3SchoolsThe querySelector() method returns the first element that matches a CSS selector. To return all matches (not only the first), use the querySelectorAll() instead. Both querySelector() and 更多内容请查看https://www.w3schools.com/jsref/met_document_queryselector.asp