<!DOCTYPE html>
<html>
<head>
<style>
div {
background-color: yellow;
padding: 20px;
display: none;
}
span:hover + div {
display: block;
</style>
</head>
<body>
<span>将鼠标悬停在我上面！</span>
<div>悬停时我将显示</div>
</body>
</html>