单击按钮时将字体大小增大或减小1em

<button id="increaseFont">增大字体</button>
<button id="decreaseFont">减小字体</button>

var increaseButton = document.getElementById("increaseFont");
var decreaseButton = document.getElementById("decreaseFont");

increaseButton.addEventListener("click", increaseFontSize);
decreaseButton.addEventListener("click", decreaseFontSize);

body {
  font-size: 16px;
}

.adjustable-font {
  /* 根据需要调整的元素选择器，例如p、h1等 */
}

function increaseFontSize() {
  var adjustableElements = document.getElementsByClassName("adjustable-font");
  for (var i = 0; i < adjustableElements.length; i++) {
    var currentSize = parseFloat(window.getComputedStyle(adjustableElements[i]).fontSize);
    adjustableElements[i].style.fontSize = (currentSize + 1) + "px";
  }
}

function decreaseFontSize() {
  var adjustableElements = document.getElementsByClassName("adjustable-font");
  for (var i = 0; i < adjustableElements.length; i++) {
    var currentSize = parseFloat(window.getComputedStyle(adjustableElements[i]).fontSize);
    adjustableElements[i].style.fontSize = (currentSize - 1) + "px";
  }
}