在慕課網上有篇css3學習課程，在里面看到了一種只要css3就可以完成的選中改變樣式的例子，在這里記錄下來。
html

<form action="#">
  <div class="wrapper">
    <div class="box">
      <input type="radio" checked="checked"  id="boy" name="1" /><span></span>
    </div>
    <label for="boy">男</label>
  </div>
  
  <div class="wrapper">
    <div class="box">
      <input type="radio"  id="girl" name="1"  /><span></span>
    </div>
    <label for="girl">女</label>
  </div>
</form>

css3

form {
  border: 1px solid #ccc;
  padding: 20px;
  width: 300px;
  margin: 30px auto;
}
.wrapper {
  margin-bottom: 10px;
}
.box {
  display: inline-block;
  width: 30px;
  height: 30px;
  margin-right: 10px;
  position: relative;
  background: orange;
  vertical-align: middle;
  border-radius: 100%;
}
.box input {
  opacity: 0;
  position: absolute;
  top:0;
  left:0;
  width: 100%;
  height:100%;
  z-index:100;/*使input按鈕在span的上一層，不加點擊區域會出現不靈敏*/
}

.box span { 
  display: block;
  width: 10px;
  height: 10px;
  border-radius: 100%;
  position: absolute;
  background: #fff;
  top: 50%;
  left:50%;
  margin: -5px 0  0 -5px;
  z-index:1;
}

input[type="radio"] + span {
  opacity: 0;

}
input[type="radio"]:checked + span {
  opacity: 1;
}

效果圖