CSS3 selectors: checked selector

In form elements, radio buttons and check buttons have a checked and unchecked state. (As we all know, these two buttons to override the default style is more difficult). In CSS3, we can state selector ": checked" with other tags to implement a custom style. The ": checked" indicates the selected state.

Example shows:

By ": checked" state from box defined effect.

HTML code

<form action="#">
  <div class="wrapper">
    <div class="box">
      <input type="checkbox" checked="checked" id="usename" /><span>√</span>
    </div>
    <lable for="usename">我是选中状态</lable>
  </div>
  
  <div class="wrapper">
    <div class="box">
      <input type="checkbox"  id="usepwd" /><span>√</span>
    </div>
    <label for="usepwd">我是未选中状态</label>
  </div>
</form> 

CSS code:

form {
  border: 1px solid #ccc;
  padding: 20px;
  width: 300px;
  margin: 30px auto;
}

.wrapper {
  margin-bottom: 10px;
}

.box {
  display: inline-block;
  width: 20px;
  height: 20px;
  margin-right: 10px;
  position: relative;
  border: 2px solid orange;
  vertical-align: middle;
}

.box input {
  opacity: 0;
  position: absolute;
  top:0;
  left:0;
}

.box span {
  position: absolute;
  top: -10px;
  right: 3px;
  font-size: 30px;
  font-weight: bold;
  font-family: Arial;
  -webkit-transform: rotate(30deg);
  transform: rotate(30deg);
  color: orange;
}

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

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