JSFiddle - React, Tailwind, and code Playground

HTML

<h1 style="text-align: center;">JavaScript 系列四：第4課 ── jQuery 套件 (原生JS)</h1>

<h1 class="title">
  Make me green
</h1>

<p class="para">
  Make me red
</p>
<p class="para">
  Me red too
</p>
<p class="para">
  Also me
</p>

JavaScript

let title = document.querySelector(".title");
title.style.color = "green";

let paras = document.querySelectorAll(".para");
for (let para of paras) {
  para.style.color = "red";
}