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问题:

Hey guys can anyone help me I need this dropdown menu in my existing navbar. The dropdown menu should be on the right hand site of the navbar. please!

This is the html body part:

<body>
    <ul class="topnav">
        <li><a class="active" href="#home">Home</a></li>
        <li><a href="#news">News</a></li>
        <li><a href="#contact">Contact</a></li>
        <li><a href="#about">About</a></li>

        <li class="dropdown, right">
            <a href="javascript:void(0)" class="dropbtn">Dropdown</a>
            <div class="dropdown-content">
                <a href="#">Link 1</a>
                <a href="#">Link 2</a>
                <a href="#">Link 3</a>
            </div>
        </li>
    </ul>
</body>

and this is my css code:

body {
    background-color: #D3D3D3; 
}

body {margin: 0;}

ul.topnav {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    position: fixed;
    top: 0;
    width: 100%;
}

ul.topnav li {float: left;}

ul.topnav li a {
    display: block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

ul.topnav li a:hover:not(.active) {
    background-color: #D3D3D3;
    color: #000;
}

ul.topnav li a.active {
    background-color: #D2691E;
    color: white;
}

ul.topnav li.right {float: right;}

@media screen and (max-width: 600px){
    ul.topnav,
    ul.topnav {position: unset}
    ul.topnav li.right, 
    ul.topnav li {float: none;}
}

回答1:

Hide the menu, then set it to position: absolute so that when it's displayed, it won't change the layout of the navbar. Then when you hover .dropdown, show the menu. Also changed the font color so the links are visible, removed overflow: hidden; from the navbar so that the menu can overflow outside of the menu and still be visible, and changed the :hover selector that changes the background color of the links to trigger on hover of the li instead of the a so that the dropdown link color stays changed as you interact with the dropdown menu.

body {
    background-color: #D3D3D3; 
}

body {margin: 0;}

ul.topnav {
    list-style-type: none;
    margin: 0;
    padding: 0;
    background-color: #333;
    position: fixed;
    top: 0;
    width: 100%;
}

ul.topnav li {float: left;}

ul.topnav li a {
    display: block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

ul.topnav li:hover a:not(.active) {
    background-color: #D3D3D3;
    color: #000;
}

ul.topnav li a.active {
    background-color: #D2691E;
    color: white;
}

ul.topnav li.right {float: right;}

@media screen and (max-width: 600px){
    ul.topnav,
    ul.topnav {position: unset}
    ul.topnav li.right, 
    ul.topnav li {float: none;}
}

ul.topnav .dropdown-content {
  display: none;
  position: absolute;
}
ul.topnav .dropdown-content a {
  color: black;
}
ul.topnav .dropdown:hover > .dropdown-content {
  display: block;
}

<ul class="topnav">
  <li><a class="active" href="#home">Home</a></li>
  <li><a href="#news">News</a></li>
  <li><a href="#contact">Contact</a></li>
  <li><a href="#about">About</a></li>

  <li class="dropdown right">
    <a href="javascript:void(0)" class="dropbtn">Dropdown</a>
    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </li>
</ul>

回答2:

Here is an example on how to build a simple drop-down menu.

<!-- HTML -->
<div class="dropdown">
  <input class="dropdown-toggle" type="text">
  <div class="dropdown-text">Account</div>
  <ul class="dropdown-content">
    <li><a href="#">Settings</a></li>
    <li><a href="#">Projects</a></li>
    <li><a href="#">Log out</a></li>
  </ul>
</div>

<!-- CSS -->

a {
  text-decoration: none;
}

.dropdown {
  position: relative;
  display: inline-block;
  text-align: left;
  width: 132px;
}

.dropdown-text {
  cursor: pointer;
  position: absolute;
  text-indent: 10px;
  line-height: 32px;
  background-color: #eee;
  border: 1px solid #ccc;
  border-radius: 3px;
  box-shadow: 0 1px 0 rgba(255,255,255, .9) inset, 0 1px 3px rgba(0,0,0, .1);
  width: 100%;
}

.dropdown-text:after {
  position: absolute;
  right: 6px;
  top: 15px;
  content: '';
  width: 0px;
  height: 0px;
  border-style: solid;
  border-width: 5px 4px 0 4px;
  border-color: #555 transparent transparent transparent;
}

.dropdown-text,
.dropdown-content a {
  color: #333;
  text-shadow: 0 1px #fff;
}

.dropdown-toggle {
  font-size: 0;
  z-index: 1;
  cursor: pointer;
  position: absolute;
  top: 0;
  border: none;
  padding: 0;
  margin: 0 0 0 1px;
  background: transparent;
  text-indent: -10px;
  height: 34px;
  width: 100%;
}

.dropdown-toggle:focus {
  outline: 0;
}

.dropdown-content {
  -webkit-transition: all .25s ease;
  -moz-transition: all .25s ease;
  -ms-transition: all .25s ease;
  -o-transition: all .25s ease;
  transition: all .25s ease;
  list-style-type: none;
  position: absolute;
  top: 32px;
  padding: 0;
  margin: 0;
  opacity: 0;
  visibility:hidden;
  border-radius: 3px;
  text-indent: 10px;
  line-height: 32px;
  background-color: #eee;
  border: 1px solid #ccc;
  width: 140px;
}

.dropdown-content a {
  display: block;
}

.dropdown-content a:hover {
  background: #e8e8e8;
}


.dropdown-toggle:hover ~ .dropdown-text,
.dropdown-toggle:focus ~ .dropdown-text {
  background-color: #e8e8e8;
}

.dropdown-toggle:focus ~ .dropdown-text {
  box-shadow: 0 1px 3px rgba(0,0,0, .2) inset, 0 1px 0 rgba(255,255,255, 0.8);
  z-index: 2;
}

.dropdown-toggle:focus ~ .dropdown-text:after {
  border-width: 0 4px 5px 4px;
  border-color: transparent transparent #555 transparent;
}

.dropdown-content:hover,
.dropdown-toggle:focus ~ .dropdown-content {
  opacity: 1;
  visibility:visible;
  top: 42px;
}

回答3:

Ok , i guess you want something like this :

ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
}

li {
    float: left;
}

li a, .dropbtn {
    display: inline-block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}

li a:hover, .dropdown:hover .dropbtn {
    background-color: red;
}

li.dropdown {
    display: inline-block;
}

.dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    z-index: 1;
}

.dropdown-content a {
    color: black;
    padding: 12px 16px;
    text-decoration: none;
    display: block;
    text-align: left;
}

.dropdown-content a:hover {background-color: #f1f1f1}

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

<!DOCTYPE html>
<html>
<head>
</head>
<body>

<ul>
  <li><a href="#home">Home</a></li>
  <li><a href="#news">News</a></li>
  <li class="dropdown">
    <a href="javascript:void(0)" class="dropbtn">Dropdown</a>
    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </li>
</ul>

<h3>Dropdown Menu inside a Navigation Bar</h3>
<p>Hover over the "Dropdown" link to see the dropdown menu.</p>

</body>
</html>

hope it helps.