我正试图在单击复选框时使用Bootstrap的折叠类来切换元素。页面加载时应取消选中复选框并显示元素。单击该框时，该元素应隐藏起来。我正试图通过"in"类来实现这一点，但无论是否包含in类，页面都以相同的方式呈现(以隐藏元素开头(。
这是我的密码。我使用Django作为后端，它使用大括号中的元素。
<!DOCTYPE html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Javascript -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
<!-- Bootstrap -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<!-- Add additional CSS in static file -->
{% load static %}
<link rel="stylesheet" href="{% static 'custom.css' %}">
<link rel="shortcut icon" href="{% static 'favicon.ico' %}">
<title>Website Vetting</title>
</head>
<body>
<h2 class="m-3">
Website Vetting
</h2>
<form method="POST" enctype="multipart/form-data" class="m-3">
{{ formset.management_form }}
{% for form in formset %}
{% csrf_token %}
<div style="max-width: 758px;"> {{ form.site }} </div>
<label data-toggle="collapse" data-target="#new-instance">
{{ form.not_found }} I didn't find anything on this website
</label>
<br>
<div id="new-instance" class="new-instance collapse in">
<p class="instance-header m-2 mt-3">Add a new instance</p>
<!-- Form data -->
</div>
{% endfor %}
<input type="submit" class="btn btn-secondary mt-3" value="Submit Report"/>
</form>
</body>
</html>
新的实例类只是：
div.new-instance {
background: rgba(175, 175, 175, .3);
border-radius: 5px;
max-width: 720px;
padding: 1px 20px 12px 20px;
}
编辑：我在看错误版本的引导程序的文档。。。诶呀
在Bootstrap 4中不再使用in类。而是使用show类。