css float如果在它上面有块级元素为什么上不去


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .same {
            width: 200px;
            height: 200px;
        }
        .left {
            background-color: yellow;
            float: left;
        }
        .right {
            background-color: red;
            float: right;
        }
        .top {
            background-color: blue;
            height: 200px;
        }
    </style>
</head>
<body>
    <div class="top">1</div>
    <div class="left same"></div>
    <div class="right same"></div>
</body>
</html>

img

本来就上不去啊，要上去你要添加position属性