如何使用+/-按钮更改站点字体大小

<button id="increaseBtn">+</button>
<button id="decreaseBtn">-</button>

var increaseBtn = document.getElementById("increaseBtn");
var decreaseBtn = document.getElementById("decreaseBtn");

increaseBtn.addEventListener("click", increaseFontSize);
decreaseBtn.addEventListener("click", decreaseFontSize);

function increaseFontSize() {
  var currentSize = parseFloat(window.getComputedStyle(document.body).fontSize);
  document.body.style.fontSize = (currentSize + 1) + "px";
}

function decreaseFontSize() {
  var currentSize = parseFloat(window.getComputedStyle(document.body).fontSize);
  document.body.style.fontSize = (currentSize - 1) + "px";
}