<h1 id="textHead" class="box">Hello</h1>
  <button id="addButton">Add Class</button>
  <button id="removeButton">Remove Class</button>
.style {
    color: green;
    padding: 10px;
  }
const boxDiv = document.querySelector("#textHead");
const addButton = document.querySelector("#addButton");
const removeButton = document.querySelector("#removeButton");

addButton.addEventListener("click", function () {
  textHead.classList.add("style");
});

removeButton.addEventListener("click", function () {
  textHead.classList.remove("style");
});

External CSS

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External JavaScript

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