jsでcssプロパティを変更する方法

<div class="test" style="height: 100px;">TEST</div>
<button class="cssText">cssText</button>
<button class="setAttribute">setAttribute</button>
<button class="stylesheet ">stylesheet </button>

.test {
   font-size: 30px;
   color: blue;
   background-color: blueviolet
}

    var testNode = document.getElementsByClassName("test")[0];
    var cssTextBtn = document.getElementsByClassName("cssText")[0];
    var attributeBtn = document.getElementsByClassName("setAttribute")[0];
    var stylesheetBtn = document.getElementsByClassName("stylesheet")[0];
    
    // 1. 修改style样式: 
    stylesheetBtn.addEventListener('click', function(e) {
        var stylesheet = document.styleSheets[0];
        stylesheet.cssRules[0].style.backgroundColor = "green";
    }, false);
    
    // 2. 修改特定元素节点的style内容
    cssTextBtn.addEventListener('click', function(e) {
        testNode.style.cssText = "width: 300px; background-color: red; height: 200px;"
        testNode.style.border = "1px solid black"
    }, true);
    
    // 3. 通过setAttribute 修改style属性值
    attributeBtn.addEventListener('click', function(e) {
        testNode.setAttribute('style', 'width: 400px; background-color: yellow; height: 300px;')
    }, false)