<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>#a:hover ~ #b {
        background: #ccc
    }</style>
</head>
<body>
    
    
    <div id="a">Div A</div>
    <div>random other elements</div>
    <div>random other elements</div>
    <div>random other elements</div>
    <div id="b">Div B</div>
</body>
</html>