如何在屏幕缩小到768像素时添加媒体查询，以便我的弹性框导航栏变为切换菜单？
我需要查询中的代码。
@media only screen and (max-width: 768px) {
}
柔性盒甚至可以吗？
请不要发布其他网站的链接。
请不要建议我使用bootstrap。我不知道如何使用它。
这是我的代码。
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
#main-nav a {
color: #ffffff;
background: #d3333b;
display: block;
height: 48px;
font-family: Arial, Helvetica, sans-serif;
font-weight: bold;
display: flex;
align-items: center;
justify-content: center;
text-decoration: none;
transition: background 0.4s;
}
#main-nav a:hover {
background: #777;
}
#main-nav ul {
list-style: none;
display: flex;
}
#main-nav li {
width: 100%;
text-align: center;
position: relative;
}
#main-nav li:hover .submenu>li {
display: block;
top: 0px;
}
.submenu li {
display: none;
position: absolute;
top: 0px;
}
.submenu {
display: flex;
flex-direction: column;
position: absolute;
width: 100%;
}
.wrapper {
margin-right: auto;
/* 1 */
margin-left: auto;
/* 1 */
max-width: 960px;
/* 2 */
padding-right: 10px;
/* 3 */
padding-left: 10px;
/* 3 */
}
@media only screen and (max-width: 768px) {
}<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Flexbox Dropdown Menu</title>
</head>
<body>
<nav id="main-nav">
<ul>
<li>
<a href="#">Home</a>
</li>
<li>
<a href="#">Menu 1</a>
<ul class="submenu">
<li>
<a href="#">Sub Menu 1.1</a>
</li>
<li>
<a href="#">Sub Menu 1.2</a>
</li>
<li>
<a href="#">Sub Menu 1.3</a>
</li>
<li>
<a href="#">Sub Menu 1.4</a>
</li>
<li>
<a href="#">Sub Menu 1.5</a>
</li>
<li>
<a href="#">Sub Menu 1.6</a>
</li>
<li>
<a href="#">Sub Menu 1.7</a>
</li>
</ul>
</li>
<li>
<a href="">Menu 2</a>
<ul class="submenu">
<li>
<a href="#">Sub Menu 2.1</a>
</li>
<li>
<a href="#">Sub Menu 2.2</a>
</li>
<li>
<a href="#">Sub Menu 2.3</a>
</li>
</ul>
</li>
<li>
<a href="#">Menu 3</a>
</li>
<li>
<a href="#">Menu 4</a>
</li>
</ul>
</nav>
</body>请试试这个css：
@media (max-width: 768px){
#main-nav ul{
flex-direction: column;
}
.submenu{
position: relative;
}
}