首先是构思

我们使用<input type="checkbox">标签来实现这个效果。
checkbox的选中、未选中的特性，刚好对应开关的打开、关闭
on:打开 off:关闭

<label for="ck2">
  <input type="checkbox" id="ck2">
  <span>未选中，则关闭开关</span>
</label>
<br>
<label for="ck1">
  <input type="checkbox" id="ck1" checked>
  <span>选中，则打开开关</span>
</label>

开始画出off、on状态的草图

这里要讲解一下，使用了position来实现的定位。有不了解的同学可以打开MDN查看相关知识

<P>off状态草图</P>
<div class="toggle">
  <div class="cookie"></div>
</div>
<br>
<P>on状态草图</P>
<div class="toggle2">
  <div class="cookie2"></div>
</div>

.toggle{
  display:inline-block;
  position:relative;
  height:25px;
  width:50px;  
  border-radius:4px;
  background:#CC0000;
}
.cookie{
  position:absolute;
  left:2px;
  top:2px;
  bottom:2px;
  width:50%;
  background:rgba(230,230,230,0.9);
  border-radius:3px;
}
.toggle2{
  display:inline-block;
  position:relative;
  height:25px;
  width:50px; 
  padding:2px;
  border-radius:4px;
  background:#66CC33;  
}
.cookie2{
  position:absolute;
  right:2px;
  top:2px;
  bottom:2px;  
  width:50%;
  background:rgba(230,230,230,0.9);
  border-radius:3px;
}

然后我们将这两个草图放到label内

<label for="ck4">
  <input type="checkbox" id="ck4">
  <div class="toggle">
    <div class="cookie"></div>
  </div>
</label>
<br>
<label for="ck3">
  <input type="checkbox" id="ck3" checked>
  <div class="toggle2">
    <div class="cookie2"></div>
  </div>
</label>

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结合label和checkbox整理、优化css

<label for="ck5">
  <input type="checkbox" id="ck5">
  <div class="toggle-finish">
    <div class="cookie-finish"></div>
  </div>
</label>
<br>
<label for="ck6">
  <input type="checkbox" id="ck6" checked>
  <div class="toggle-finish">
    <div class="cookie-finish"></div>
  </div>
</label>

.toggle-finish{
  cursor:pointer;
  display:inline-block;
  position:relative;
  height:25px;
  width:50px;  
  border-radius:4px;
  background:#CC0000;
}
.cookie-finish{
  position:absolute;
  left:2px;
  top:2px;
  bottom:2px;
  width:50%;
  background:rgba(230,230,230,0.9);
  border-radius:3px;
}
input:checked + .toggle-finish{
  background:#66CC33;  
}
input:checked + .toggle-finish .cookie-finish{ 
  left:auto;
  right:2px;
}

到此为止就已经基本实现一个开关的功能了，记得将input隐藏起来哦

css实现开关效果