上下固定中间自适应.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        .c1,.c3{
            height: 20px;
            background: pink;
        }
        .c2{
            /*padding: ;*/
        }
    </style>
</head>
<body>
    <div class="c1"></div>
    <div class="c2"></div>
    <div class="c3"></div>
</body>
</html>