【children_index】
<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
.parent {
background: red;
margin: 20px;
padding: 20px;
}
.child {
background: blue;
margin: 20px;
padding: 20px;
}
.parent:hover .child {
background: yellow;
}
</style>
</head>
<body>
<div class="parent">
<div class="child"></div>
</div>
<div class="parent">
<div class="child"></div>
</div>
</body>
</html>
