可以通过JS实现 $(this).find("span").css('color','red');方式更改，通过CSS更改也是可以的
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
div {
width:500px;height:500px;background:pink;position: relative;
}
span {
width:100px;height:100px;display:block;position: absolute;top:100px;left:100px;
background:#ddd;
transition:1s;
}
div a:hover span {
background-color: #777;
}
div a {
color:red;
transition:1s;
}
div a:hover {
color:#000;
}
</style>
</head>
<body>
<div>
<a href="#">
<span></span>
BACK TO TOP
</a>
</div>
</body>
</html>