자바스크립트가 웹페이지 스타일을 변경할 수 있나요?

.style1 {
    margin: 10px auto;
    background - color: #9999FF;
    display: block;
    color: White;
    border: 1px solid white;
    padding: 10px 25px;
    font - size: 18px;
}
.style1: hover {
    background - color: #66B3FF;
    cursor: pointer;
}
.style2 {
    margin: 10px auto;
    background - color: gray;
    display: block;
    color: black;
    border: 1px solid white;
    padding: 10px25px;
    font - size: 18px;
}
.style2: hover {
    background - color: black;
    color: White;
    cursor: pointer
}

<div>
  <input id="btnB" type="button" name="btnLogin" value="登录" class="style1" />
  <div id="tool">
    <input type="button" value="【obj.style.className】更改样式" onclick="changeBackgroundColor()" />
    <input type="button" value="【obj.style.cssText】更改样式" onclick="changeFontSize()" />
    <input type="button" value="【obj.className】更改样式" onclick="addRadius()" />
    <input type="button" value="更改外联css样式" onclick="recover()" /></div>
</div>

function changeStyle2() {
   var obj = document.getElementById("btnB");
   obj.style.cssText = " display:block;color:White;
 
}

function changeStyle3() {
  var obj = document.getElementById("btnB");
  //obj.className = "style2";
  obj.setAttribute("class", "style2");
}

<link href="css1.css" rel="stylesheet" type="text/css" id="css"/>
 
function changeStyle4() {
   var obj = document.getElementById("css");
   obj.setAttribute("href","css2.css");
 }