Div 元素未显示在页面上，即使在检查元素之后

Question

我有一个站点，应该适用于手机和PC，但我还没有添加后者。问题是，我有两个带有 class="row" 的标签，但只有第一个出现（在您使页面足够小之后）。代码：

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="api/reponse-api-2.css">
    <link rel="stylesheet" href="css/index.css">
</head>
<body class="nomargin">
    <!--MOBILE VERSION-->
    <div class="size-small">
        <div class="row"><iframe frameBorder="0" src="html/header-small.html" class="col-12" height="100px"/></div>
        <div class="row">
            <div class="col-12 checkbox-mobile">
                <form>
                <input type="checkbox">Embed site in browser</input>
                </form>
            </div>
        </div>
    </div>

    <!--TABLET VERSION-->
    <div class="size-medium">
        tablet
    </div>

    <!--PC VERSION-->
    <div class="size-large">
        pc
    </div>
</body>

Answer 1

语法错误 HTML:

<div class="size-small">
       <!-- The iframe must be closed </iframe> -->
       <!-- (if bootstrap) The class col-12 is col-sm-12 or col-md-12 or col-xs-12 (NOT col-12)  -->
        <div class="row"><iframe frameBorder="0" src="html/header-small.html" class="col-12" height="100px"></iframe></div>
        <div class="row">
            <div class="col-12 checkbox-mobile">
                <form>
                <!-- The input close is wrong. -->
                <!-- <input type="checkbox">BAD</input> -->
                     <input type="checkbox">GOOD
                </form>
            </div>
        </div>
    </div>

Div 元素未显示在页面上，即使在检查元素之后

Div element not showing up on page, even after inspect element

html

invisible