html - 如何在菜单顶部制作此警告栏

Question

当我试图把这个 alert bar在我的网站上，我发现它被我的菜单重叠了。一些文章说 z-index 和 position:absolute 可以将一个元素放在另一个元素之上，但这在这种情况下不起作用。我想知道如何将警告栏放在菜单上。感谢您的帮助。

这是一个 fiddle这说明了问题。

CSS:

body {
    padding: 0;
}

/* Alert Bar*/

#alert {
    position: relative;
}
#alert:hover:after {
    background: hsla(0,0%,0%,.8);
    border-radius: 3px;
    color: #f6f6f6;
    content: 'Click to dismiss';
    font: bold 12px/30px sans-serif;
    height: 30px;
    left: 50%;
    margin-left: -60px;
    position: absolute;
    text-align: center;
    top: 50px;
    width: 120px;
}
#alert:hover:before {
    border-bottom: 10px solid hsla(0,0%,0%,.8);
    border-left: 10px solid transparent;
    border-right: 10px solid transparent;
    content: '';
    height: 0;
    left: 50%;
    margin-left: -10px;
    position: absolute;
    top: 40px;
    width: 0;
}
#alert:target {
    display: none;
}
.alert {
    background-color: #c4453c;
    background-image: -webkit-linear-gradient(135deg, transparent,
                      transparent 25%, hsla(0,0%,0%,.05) 25%,
                      hsla(0,0%,0%,.05) 50%, transparent 50%,
                      transparent 75%, hsla(0,0%,0%,.05) 75%,
                      hsla(0,0%,0%,.05));
    background-image: -moz-linear-gradient(135deg, transparent,
                      transparent 25%, hsla(0,0%,0%,.1) 25%,
                      hsla(0,0%,0%,.1) 50%, transparent 50%,
                      transparent 75%, hsla(0,0%,0%,.1) 75%,
                      hsla(0,0%,0%,.1));
    background-image: -ms-linear-gradient(135deg, transparent,
                      transparent 25%, hsla(0,0%,0%,.1) 25%,
                      hsla(0,0%,0%,.1) 50%, transparent 50%,
                      transparent 75%, hsla(0,0%,0%,.1) 75%,
                      hsla(0,0%,0%,.1));
    background-image: -o-linear-gradient(135deg, transparent,
                      transparent 25%, hsla(0,0%,0%,.1) 25%,
                      hsla(0,0%,0%,.1) 50%, transparent 50%,
                      transparent 75%, hsla(0,0%,0%,.1) 75%,
                      hsla(0,0%,0%,.1));
    background-image: linear-gradient(135deg, transparent,
                      transparent 25%, hsla(0,0%,0%,.1) 25%,
                      hsla(0,0%,0%,.1) 50%, transparent 50%,
                      transparent 75%, hsla(0,0%,0%,.1) 75%,
                      hsla(0,0%,0%,.1));
    background-size: 20px 20px;
    box-shadow: 0 5px 0 hsla(0,0%,0%,.1);
    color: #f6f6f6;
    display: block;
    font: bold 16px/40px sans-serif;
    height: 40px;
    position: absolute;
    text-align: center;
    text-decoration: none;
    top: -45px;
    width: 100%;
    -webkit-animation: alert 1s ease forwards;
       -moz-animation: alert 1s ease forwards;
        -ms-animation: alert 1s ease forwards;
         -o-animation: alert 1s ease forwards;
            animation: alert 1s ease forwards;
}

/* Animation */

@-webkit-keyframes alert {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { top: 0; }
}
@-moz-keyframes alert {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { top: 0; }
}
@-ms-keyframes alert {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { top: 0; }
}
@-o-keyframes alert {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { top: 0; }
}
@keyframes alert {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { top: 0; }
}

/* Menu*/
#cssmenu {padding: 0; margin: 0; border: 0;}
#cssmenu ul, #cssmenu li {list-style: none; margin: 0; padding: 0;}
#cssmenu ul {position: relative; z-index: 597; }
#cssmenu ul li { float: left; min-height: 1px; vertical-align: middle;}
#cssmenu ul li.hover,
#cssmenu ul li:hover {position: relative; z-index: 599; cursor: default;}
#cssmenu ul ul {visibility: hidden; position: absolute; top: 100%; left: 0; z-index: 598;}
#cssmenu ul ul li {float: none;}
#cssmenu ul ul ul {top: 0; left: auto; right: -99.5%; }
#cssmenu ul li:hover > ul { visibility: visible;}
#cssmenu ul ul {bottom: 0; left: 0;}
#cssmenu ul ul {margin-top: 0; }
#cssmenu ul ul li {font-weight: normal;}
#cssmenu a { display: block; line-height: 1em; text-decoration: none; }

#cssmenu {
  background: #333;
  border-bottom: 4px solid #1b9bff;
  font-family: 'Oxygen Mono', Tahoma, Arial, sans-serif;
  font-size: 12px; 
}

  #cssmenu > ul { *display: inline-block; }

  #cssmenu:after, #cssmenu ul:after {
    content: '';
    display: block;
    clear: both; 
}

#cssmenu a {
    background: #333;
    color: #CBCBCB;
    padding: 0 20px; 
}
#cssmenu ul { text-transform: uppercase; }

    #cssmenu ul ul {
      border-top: 4px solid #1b9bff;
      text-transform: none;
      min-width: 190px; 
}
      #cssmenu ul ul a {
        background: #1b9bff;
        color: #FFF;
        border: 1px solid #0082e7;
        border-top: 0 none;
        line-height: 150%;
        padding: 16px 20px; 
}
      #cssmenu ul ul ul { border-top: 0 none; }

      #cssmenu ul ul li { position: relative }

#cssmenu > ul > li > a { line-height: 48px;  }

#cssmenu ul ul li:first-child > a { border-top: 1px solid #0082e7; }
        #cssmenu ul ul li:hover > a { background: #35a6ff; }

        #cssmenu ul ul li:last-child > a {
          border-radius: 0 0 3px 3px;
          box-shadow: 0 1px 0 #1b9bff; 
}
        #cssmenu ul ul li:last-child:hover > a { border-radius: 0 0 0 3px; }

        #cssmenu ul ul li.has-sub > a:after {
          content: '+';
          position: absolute;
          top: 50%;
          right: 15px;
          margin-top: -8px;
}

    #cssmenu ul li:hover > a, #cssmenu ul li.active > a {
      background: #1b9bff;
      color: #FFF;
}
    #cssmenu ul li.has-sub > a:after {
      content: '+';
      margin-left: 5px; 
}
    #cssmenu ul li.last ul {
      left: auto;
      right: 0; 
}
      #cssmenu ul li.last ul ul {
        left: auto;
        right: 99.5%;
}

HTML:

<div id="alert">
    <a class="alert" href="#alert"> Alert Bar overlapped</a>
</div>



<div id='cssmenu'>
  <ul>
     <li class='has-sub '><a href="#">XXX</a>
     <ul>
     <li><a href="#">XXX</a></li>
     <li><a href="#">XXX</a></li>
     <li><a href="#">XXX</a></li>
     <li><a href="#">XXX</a></li> 
     <li><a href="#">XXX</a></li>          
 </ul>
</li>
     <li class='has-sub '><a href="#">XXX</a>
        <ul>
           <li><a href="#">XXX</a></li>
           <li><a href="#" class="messages">XXX</a></li>                              
           <li><a href="#">XXX</a></li> 
           <li><a href="#" class="documents">XXX</a>
           <ul>
              <li><a href="#" class="documents">XXX</a></li>
              <li><a href="#" class="documents">XXX</a></li>
           </ul>
         </li>
      </ul>
     </li>           
     <li><a href="#">XXX</a></li>
   <li class='has-sub'><a href="#">XXX</a>
      <ul>
         <li><a href="#">XXX</a></li>

      </ul>
   </li>
     <li><a href="#">XXX</a></li>

  </ul>
</div>

Answer 1

将 z-index 值更改为 9999

#alert {
    position: relative;
    z-index: 9999;
}