如何解决使用JavaScript和CSS定位子菜单
如何使包装盒具有响应性？例如，最后一个子菜单超出边界。我不知道如何验证盒子是否在空间中可见以及如何正确移动它们。在这种情况下，我想了解如何在不可见的情况下移动第二层，或者在第二层和第三层都可见但仅第三层不可见时如何移动第二层和第三层。
document.addEventListener('click',function(e) {
e = e || window.event;
console.log(e);
var target = e.target || e.srcElement;
console.log(target);
if (target.parentElement.className.indexOf('has-submenu') > -1) {
e.target.classList.toggle('open');
}
},false);#menu {
background: #343434;
color: #eee;
height: 35px;
border-bottom: 4px solid #eeeded
}
#menu ul,#menu li {
margin: 0 0;
padding: 0 0;
list-style: none
}
#menu ul {
height: 35px
}
#menu li {
float: left;
display: inline;
position: relative;
font: bold 12px Arial;
text-shadow: 0 -1px 0 #000;
border-right: 1px solid #444;
border-left: 1px solid #111;
text-transform: uppercase
}
#menu li:first-child {
border-left: none
}
#menu a {
display: block;
line-height: 35px;
padding: 0 14px;
text-decoration: none;
color: #eee;
}
#menu li:hover > a,#menu li a:hover {
background: #111
}
#menu input {
display: none;
margin: 0 0;
padding: 0 0;
width: 80px;
height: 35px;
opacity: 0;
cursor: pointer
}
#menu label {
font: bold 30px Arial;
display: none;
width: 35px;
height: 36px;
line-height: 36px;
text-align: center
}
#menu label span {
font-size: 12px;
position: absolute;
left: 35px
}
#menu ul.menus {
height: auto;
width: 180px;
background: #111;
position: absolute;
z-index: 99;
display: none;
border: 0;
}
#menu ul.menus li {
display: block;
width: 100%;
font: 12px Arial;
text-transform: none;
}
#menu li:hover ul.menus {
display: block
}
#menu a.home {
background: #c00;
}
#menu a.prett {
padding: 0 27px 0 14px
}
#menu a.prett::after {
content: "";
width: 0;
height: 0;
border-width: 6px 5px;
border-style: solid;
border-color: #eee transparent transparent transparent;
position: absolute;
top: 15px;
right: 9px
}
#menu a.prett.open::after {
content: "";
width: 0;
height: 0;
border-width: 6px 5px;
border-style: solid;
border-color: transparent transparent #eee transparent;
position: absolute;
top: 9px;
right: 9px
}
#menu ul.menus a:hover {
background: #333;
}
#menu ul.menus .submenu {
display: none;
position: absolute;
left: 180px;
background: #111;
top: 0;
width: 180px;
}
#menu ul.menus .submenu li {
background: #111;
}
#menu ul.menus .has-submenu a.open ~ .submenu {
display: block;
}<nav>
<ul id='menu'>
<li><a class='home' href='/'>Home</a></li>
<li><a class='prett' href='#' title='Menu'>Menu</a>
<ul class='menus'>
<li class='has-submenu'><a class='prett' title='Dropdown 1'>Dropdown 1 + Sub Menu</a>
<ul class='submenu'>
<li><a href="#" title="Sub Menu">Sub Menu</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 2</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 3</a></li>
</ul>
</li>
<li><a href='#' title='Dropdown 2'>Dropdown 2</a></li>
<li><a href='#' title='Dropdown 3'>Dropdown 3</a></li>
</ul>
</li>
<li><a class='prett' href='#' title='Menu'>Menu</a>
<ul class='menus'>
<li class='has-submenu'><a class='prett' title='Dropdown 1'>Dropdown 1 + Sub Menu</a>
<ul class='submenu'>
<li><a href="#" title="Sub Menu">Sub Menu</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 2</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 3</a></li>
</ul>
</li>
<li><a href='#' title='Dropdown 2'>Dropdown 2</a></li>
<li><a href='#' title='Dropdown 3'>Dropdown 3</a></li>
</ul>
</li>
<li><a class='prett' href='#' title='Menu'>Menu</a>
<ul class='menus'>
<li class='has-submenu'><a class='prett' title='Dropdown 1'>Dropdown 1 + Sub Menu</a>
<ul class='submenu'>
<li><a href="#" title="Sub Menu">Sub Menu</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 2</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 3</a></li>
</ul>
</li>
<li><a href='#' title='Dropdown 2'>Dropdown 2</a></li>
<li><a href='#' title='Dropdown 3'>Dropdown 3</a></li>
</ul>
</li>
<li><a class='prett' href='#' title='Menu'>Menu</a>
<ul class='menus'>
<li class='has-submenu'><a class='prett' title='Dropdown 1'>Dropdown 1 + Sub Menu</a>
<ul class='submenu'>
<li><a href="#" title="Sub Menu">Sub Menu</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 2</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 3</a></li>
</ul>
</li>
<li><a href='#' title='Dropdown 2'>Dropdown 2</a></li>
<li><a href='#' title='Dropdown 3'>Dropdown 3</a></li>
</ul>
</li>
<li><a class='prett' href='#' title='Menu'>Menu</a>
<ul class='menus'>
<li class='has-submenu'><a class='prett' title='Dropdown 1'>Dropdown 1 + Sub Menu</a>
<ul class='submenu'>
<li><a href="#" title="Sub Menu">Sub Menu</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 2</a></li>
<li><a href="#" title="Sub Menu">Sub Menu 3</a></li>
</ul>
</li>
<li><a href='#' title='Dropdown 2'>Dropdown 2</a></li>
<li><a href='#' title='Dropdown 3'>Dropdown 3</a></li>
</ul>
</li>
</ul>
</nav>示例
https://jsfiddle.net/mwb2caht/
image of submenu before fix and after
解决方法
在此处使用有关 @media 查询的信息。 您可以为特定的屏幕尺寸指定指定的属性
https://www.w3schools.com/css/css3_mediaqueries_ex.asp
编辑：您可以在浏览器窗口（在Chrome上）中按 F12 ，然后按 ctrl + shift + M 以获取响应的“测试器”
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