html - 如何添加平滑的 CSS 下拉菜单

Question

我设法使用 CSS 创建了一个带有下拉菜单(子菜单)的菜单。但是我无法在我的编码中添加平滑的下拉菜单效果。我尝试添加 -moz-transition 等等。我不知道在哪里添加这些过渡以使我的正常下拉菜单成为平滑的下拉菜单效果。

下面是我的HTML编码

<div id='cssmenu'>
<ul>
   <li class='active'><a href='index.html'><span>Home</span></a></li>
   <li class='has-sub'><a href='#'><span>Products</span></a>
      <ul>
         <li class='has-sub'><a href='#'><span>Product 1</span></a>
            <ul>
               <li><a href='#'><span>Sub Item</span></a></li>
               <li class='last'><a href='#'><span>Sub Item</span></a></li>
            </ul>
         </li>
         <li class='has-sub'><a href='#'><span>Product 2</span></a>
            <ul>
               <li><a href='#'><span>Sub Item</span></a></li>
               <li class='last'><a href='#'><span>Sub Item</span></a></li>
            </ul>
         </li>
      </ul>
   </li>
   <li><a href='#'><span>About</span></a></li>
   <li class='last'><a href='#'><span>Contact</span></a></li>
</ul>
</div>

这是CSS

<style media="screen" type="text/css">
    #cssmenu ul,
    #cssmenu li,
    #cssmenu span,
    #cssmenu a {
      margin: 0;
      padding: 0;
      position: relative;
    }
    #cssmenu {
      height: 49px;
      border-radius: 5px 5px 0 0;
      -moz-border-radius: 5px 5px 0 0;
      -webkit-border-radius: 5px 5px 0 0;
      background: #fefefe;
      background: -moz-linear-gradient(top, #fefefe 0%, #eee9f0 100%);
      background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #fefefe), color-stop(100%, #eee9f0));
      background: -webkit-linear-gradient(top, #fefefe 0%, #eee9f0 100%);
      background: -o-linear-gradient(top, #fefefe 0%, #eee9f0 100%);
      background: -ms-linear-gradient(top, #fefefe 0%, #eee9f0 100%);
      background: linear-gradient(top, #fefefe 0%, #eee9f0 100%);
      border-bottom: 2px solid #db000b;
      width: auto;
    }
    #cssmenu:after,
    #cssmenu ul:after {
      content: '';
      display: block;
      clear: both;
    }
    #cssmenu a {
      background: #fefefe;
      background: -moz-linear-gradient(top, #fefefe 0%, #ececec 100%);
      background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #fefefe), color-stop(100%, #ececec));
      background: -webkit-linear-gradient(top, #fefefe 0%, #ececec 100%);
      background: -o-linear-gradient(top, #fefefe 0%, #ececec 100%);
      background: -ms-linear-gradient(top, #fefefe 0%, #ececec 100%);
      background: linear-gradient(top, #fefefe 0%, #ececec 100%);
      color: #000;
      display: inline-block;
      font-family: Helvetica, Arial, Verdana, sans-serif;
      font-size: 12px;
      line-height: 49px;
      padding: 0 20px;
      text-decoration: none;
    }
    #cssmenu ul {
      list-style: none;
    }
    #cssmenu > ul {
      float: left;
    }
    #cssmenu > ul > li {
      float: left;
    }
    #cssmenu > ul > li > a {
      color: #000;
      font-size: 12px;
    }
    #cssmenu > ul > li:hover:after {
      content: '';
      display: block;
      width: 0;
      height: 0;
      position: absolute;
      left: 50%;
      bottom: 0;
      border-left: 10px solid transparent;
      border-right: 10px solid transparent;
      border-bottom: 10px solid #db000b;
      margin-left: -10px;
    }
    #cssmenu > ul > li:first-child > a {
      border-radius: 5px 0 0 0;
      -moz-border-radius: 5px 0 0 0;
      -webkit-border-radius: 5px 0 0 0;
    }
    #cssmenu > ul > li.active:after {
      content: '';
      display: block;
      width: 0;
      height: 0;
      position: absolute;
      left: 50%;
      bottom: 0;
      border-left: 10px solid transparent;
      border-right: 10px solid transparent;
      border-bottom: 10px solid #db000b;
      margin-left: -10px;
    }
    #cssmenu > ul > li.active > a {
      -moz-box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
      -webkit-box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
      box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
      background: #ececec;
      background: -moz-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #ececec), color-stop(100%, #ffeeff ef));
      background: -webkit-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -o-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -ms-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
    }
    #cssmenu > ul > li:hover > a {
      background: #ececec;
      background: -moz-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #ececec), color-stop(100%, #ffeeff ef));
      background: -webkit-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -o-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: -ms-linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      background: linear-gradient(top, #ececec 0%, #ffeeff ef 100%);
      -moz-box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
      -webkit-box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
      box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
    }
    #cssmenu .has-sub {
      z-index: 1;
    }
    #cssmenu .has-sub:hover > ul {
      display: block;
    }
    #cssmenu .has-sub ul {
      display: none;
      position: absolute;
      width: 200px;
      top: 100%;
      left: 0;
    }
    #cssmenu .has-sub ul li {
      *margin-bottom: -1px;
    }
    #cssmenu .has-sub ul li a {
      background: #db000b;
      border-bottom: 1px dotted #ff0f1b;
      filter: none;
      font-size: 11px;
      display: block;
      line-height: 120%;
      padding: 10px;
      color: #ffffff;
    }
    #cssmenu .has-sub ul li:hover a {
      background: #a80008;
    }
    #cssmenu .has-sub .has-sub:hover > ul {
      display: block;
    }
    #cssmenu .has-sub .has-sub ul {
      display: none;
      position: absolute;
      left: 100%;
      top: 0;
    }
    #cssmenu .has-sub .has-sub ul li a {
      background: #a80008;
      border-bottom: 1px dotted #ff0f1b;
    }
    #cssmenu .has-sub .has-sub ul li a:hover {
      background: #8f0007;
    }
    </style>

Answer 1

当您写“流畅的 CSS 菜单”时，您的意思是没有 javascript 而只有 CSS？

如果是这样，请使用 css level 3 transition。

#cssmenu ul ul { 
    /* this will apply to inner UL, adapt to your desired selector */
    -webkit-transition: height 0.3s ease-in-out;
    -o-transition: height 0.3s ease-in-out;
    -moz-transition: height 0.3s ease-in-out;
    transition: height 0.3s ease-in-out;
}

[编辑]

如果它不适用于您的上下文，可能是因为您的内部 UL 元素没有“高度”。

#cssmenu .has-sub:hover > ul {
  display: block;
  height:auto; /* add this */
}
#cssmenu .has-sub ul {
  display: none;
  position: absolute;
  width: 200px;
  height:0; /* add this */
  top: 100%;
  left: 0;
}

有关跨浏览器解决方案主题的更多信息，请在网上搜索 css transition generator