悬停内容不显示在下拉菜单(网页设计)

我正在写一个网页和下拉菜单按钮不工作。悬停内容不显示。有人能告诉我原因吗?非常感谢!!

代码

* {
box-sizing: border-box;
font-family: Arial, Helvetica, sans-serif;
}
h1.header {
text-align: center;
color: #66F3ED;
}
body {
margin: 0;
}
ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: #808080;
height: 70px;
font-size: 18px;
}
li {
float: left;
height: 70px;
}
li:last-child {
border-bottom: none;
}
li a {
display: block;
color: #66f3ed;
text-align: center;
padding: 23px 60px;
text-decoration: none;
}
li a:hover:not(.active) {
background-color: #111;
}
.active {
background-color: #808080;
border-bottom: 5px solid #66f3ed;
}
/* Create three unequal columns that floats next to each other */
.column {
float: left;
height: 800px;
}
/* Left and right column */
.column.side {
width: 6%;
background-color: #868686;
overflow: hidden;
z-index:2;
}
/* Middle column */
.column.middle {
width: 70%;
background-color: #777777;
z-index:1;
}
.column.right {
width: 24%;
background-color: #919191;
}
/* Clear floats after the columns */
.row:after {
content: "";
display: table;
clear: both;
}
/*Drop down Menu*/
.dropbtn {
background-color: transparent;
color: #66F3ED;
padding: 16px;
font-size: 16px;
border: none;
}
.dropdown {
display: inline-block;
z-index: 10!important;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f1f1f1;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
left:100%;
}
.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
}

/* Responsive layout - makes the three columns stack on top of each other instead of next to each other */
@media screen and (max-width: 600px) {
.column.side, .column.middle {
width: 100%;
}
}

<!DOCTYPE html>
<html lang="en">
<head>
<title>CSS Website Layout</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="style.css">
</head>
<body>
<div class="row">
<!--Side Menu Bar-->
<div class="column side">
<div class="dropdown">
<button class="dropbtn"><img src="Menu/Menu-1.png" style="width: 100%" alt="Menu"></button>
</div>

<br /><br />
<img src="menu.jpg" alt="Menu">
</div>
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
</div>
<div class="column middle">
<ul>
<li><img src="sa_crop.gif" style="height: 70px"alt="Logo"></li> 
<li><a class="active" href="#home">Face Mask Detection</a></li>
<li><a href="#news">Social Distance Detection</a></li>
</ul>
<br /><h1 class="header">Face Mask Detection</h1><br />
<!--Face Mask Detection Area-->
</div>
<div class="column right">
<ul>
<li style="float:right"><img src="user_808080.jpg" style="height: 70px" alt="User"></li> 
</ul>

</div>
</div>
</body>
</html>

完整的编码如上所示。我不确定是什么问题，但应该是CSS样式问题。请有人给我提示一下。非常感谢!

你的HTML和CSS都有几个问题需要解决，这样菜单才能正常工作。

:<div class="dropdown">应包含</div>

中的按钮、图像和下拉菜单内容。例如，修改为:

<div class="column side">
<div class="dropdown">
<button class="dropbtn"><img src="Menu/Menu-1.png" style="width: 100%" alt="Menu"></button>
</div>

<br /><br />
<img src="menu.jpg" alt="Menu">
</div>
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
</div>

<div class="column side">
<div class="dropdown">
<button class="dropbtn"><img src="Menu/Menu-1.png" style="width: 100%" alt="Menu"></button>

<br /><br />
<img src="menu.jpg" alt="Menu">
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
</div>
</div>
</div>

第二:在.dropdown-content的风格中，使用position: absolute;是正确的，但您应该将left:100%;更改为left:0;，因此您可以在菜单项旁边获得下拉内容。

第三:添加悬停在菜单项上的CSS样式代码，使子菜单项显示为:

.dropdown:hover .dropdown-content{
display: block;
}

第四:悬停时更改子菜单项的背景，例如

.dropdown-content a:hover {
color: white;
background-color: red;
}

如果你做到了以上四点，菜单就会像预期的那样运行。

，这里是问题的完整修改代码-只需按下面的Run the code snippet:

* {
box-sizing: border-box;
font-family: Arial, Helvetica, sans-serif;
}
h1.header {
text-align: center;
color: #66F3ED;
}
body {
margin: 0;
}
ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: #808080;
height: 70px;
font-size: 18px;
}
li {
float: left;
height: 70px;
}
li:last-child {
border-bottom: none;
}
li a {
display: block;
color: #66f3ed;
text-align: center;
padding: 23px 60px;
text-decoration: none;
}
li a:hover:not(.active) {
background-color: #111;
}
.active {
background-color: #808080;
border-bottom: 5px solid #66f3ed;
}
/* Create three unequal columns that floats next to each other */
.column {
float: left;
height: 800px;
}
/* Left and right column */
.column.side {
width: 6%;
background-color: #868686;
overflow: hidden;
z-index:2;
}
/* Middle column */
.column.middle {
width: 70%;
background-color: #777777;
z-index:1;
}
.column.right {
width: 24%;
background-color: #919191;
}
/* Clear floats after the columns */
.row:after {
content: "";
display: table;
clear: both;
}
/*Drop down Menu*/
.dropbtn {
background-color: transparent;
color: #66F3ED;
padding: 16px;
font-size: 16px;
border: none;
}
.dropdown {
display: inline-block;
z-index: 10!important;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f1f1f1;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
left:0;    /* Modified */
}
.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
}
/* adding */
.dropdown:hover .dropdown-content{
display: block;
}
/* adding */
.dropdown-content a:hover {
color: white;
background-color: red;

/* Responsive layout - makes the three columns stack on top of each other instead of next to each other */
@media screen and (max-width: 600px) {
.column.side, .column.middle {
width: 100%;
}
}

<!DOCTYPE html>
<html lang="en">
<head>
<title>CSS Website Layout</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="style.css">
</head>
<body>
<div class="row">
<!--Side Menu Bar-->
<div class="column side">
<div class="dropdown">
<button class="dropbtn"><img src="Menu/Menu-1.png" style="width: 100%" alt="Title"></button>

<br /><br />
<img src="menu.jpg" alt="MenuItem">
<div class="dropdown-content">
<a href="#">Link 1</a>
<a href="#">Link 2</a>
</div>
</div>
</div>
<div class="column middle">
<ul>
<li><img src="sa_crop.gif" style="height: 70px"alt="Logo"></li> 
<li><a class="active" href="#home">Face Mask Detection</a></li>
<li><a href="#news">Social Distance Detection</a></li>
</ul>
<br /><h1 class="header">Face Mask Detection</h1><br />
<!--Face Mask Detection Area-->
</div>
<div class="column right">
<ul>
<li style="float:right"><img src="user_808080.jpg" style="height: 70px" alt="User"></li> 
</ul>

</div>
</div>
</body>
</html>

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