如何将过渡添加到W3中的下拉菜单

Question

我正在尝试根据W3的示例进行下拉菜单。我可以用作下拉菜单，但似乎无法添加过渡。我希望下拉可以放松。

我尝试在.dropdown-content类中添加transition: all 0.3s;。我还研究了许多其他下拉示例，但没有一个导致答案。

function myFunction() {
  var x = document.getElementById("myTopnav");
  if (x.className === "topnav") {
    x.className += " responsive";
  } else {
    x.className = "topnav";
  }
}

.dropbtn:hover {
  transform: scale(1.02);
  color: gray !important;
  transition: all 0.5s ease;
}
.topnav a:hover {
  transform: scale(1.02);
  color: gray;
}
@media screen and (min-width: 769px) {
  .topnav {
    overflow: hidden;
    margin-top: 3em;
    padding-top: 0.5em;
    display: inline;
    float: left;
    margin-right: 3.5%;
    margin-left: 0;
    margin-right: 0;
    float: right;
    text-align: right;
    clear: right;
    margin-top: 3em;
    padding-top: 1em;
    padding-bottom: 0.5em;
  }
  .topnav a {
    float: left;
    padding-bottom: 2em;
  }
  .dropdown:hover .dropdown-content {
    display: flex;
    border-bottom: 2px solid #d51045;
    border-top: 2px solid #d51045;
  }
}
@media screen and (max-width: 769px) {
  .topnav {
    position: relative;
    padding-bottom: 1em;
    padding-top: 1em;
  }
  .topnav .icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  .topnav a {
    float: none;
    display: block;
    text-align: center;
  }
  .topnav .dropdown {
    float: none;
  }
  .topnav .dropdown-content {
    position: relative;
    float: none;
    text-align: center;
  }
  .topnav .dropdown .dropbtn {
    display: block;
    width: 100%;
    text-align: center;
  }
  .dropdown-content a {
    float: none !important;
    text-align: center !important;
  }
  .dropdown:hover .dropdown-content {
    display: block;
  }
}
.topnav a {
  display: block;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  text-transform: uppercase;
  font-weight: 600;
  font-size: 14px;
  color: #444444;
}
.topnav .icon {
  display: none;
}
.dropdown {
  float: left;
  overflow: hidden;
}
.dropdown .dropbtn {
  border: none;
  outline: none;
  padding: 14px 16px;
  background-color: white;
  font-family: inherit;
  margin: 0;
  text-transform: uppercase;
  font-weight: 600;
  font-size: 14px;
  color: #444444;
  transition: color .2s ease-in;
}
.dropdown-content {
  display: none;
  /*box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);*/
  z-index: 1;
  background-color: white;
  position: fixed;
  top: auto;
  right: 0;
  width: 100%;
  border-bottom: 2px solid #d51045;
  border-top: 2px solid #d51045;
}
.dropdown-content a {
  float: right;
  padding: 20px 23px;
  text-decoration: none;
  display: block;
  text-align: left;
  margin: 0 auto;
}
body.home .site-header .container {
  padding-bottom: 1em;
}
img.nav-img {
  display: block;
  margin-left: auto;
  margin-right: auto;
}

<div class="topnav" id="myTopnav">
  <a href="#home" class="active"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Calendar</a>
  <div class="dropdown">
    <button class="dropbtn"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">About 
          <i class="fa fa-caret-down"></i>
             </button>
    <div class="dropdown-content">
      <a href="#">Musicians</a>
      <a href="#">More</a>
    </div>
  </div>
  <div class="dropdown">
    <button class="dropbtn"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Tickets 
          <i class="fa fa-caret-down"></i>
        </button>
    <div class="dropdown-content">
      <a href="#">Series Subscriptions</a>
      <a href="#">More</a>
    </div>
  </div>
  <div class="dropdown">
    <button class="dropbtn"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Community
          <i class="fa fa-caret-down"></i>
        </button>
    <div class="dropdown-content">
      <a href="#">Learning Programs</a>
    </div>
  </div>
  <div class="dropdown">
    <button class="dropbtn"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Visit
          <i class="fa fa-caret-down"></i>
        </button>
    <div class="dropdown-content">
      <a href="#">Seating Charts</a>
      <a href="#">Frequently Asked Questions</a>
    </div>
  </div>
  <div class="dropdown">
    <button class="dropbtn"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Give
          <i class="fa fa-caret-down"></i>
        </button>
    <div class="dropdown-content">
      <a href="#">Ways to Give</a>
      <a href="#">More</a>
    </div>
  </div>
  <a href="#" class="active"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/SNice.svg/220px-SNice.svg.png" height="22" class="nav-img">Shop</a>
  <a href="javascript:void(0);" style="font-size:15px;" class="icon" onclick="myFunction()">&#9776;</a>
</div>

我希望下拉列表具有平稳的过渡，类似于laphil.org菜单。

Answer 1

问题在CSS显示属性中。您想动画下拉的外观，但不能使用显示器进行动画。相反，我建议您使用可见性和不透明度。

.dropdown-content {
  display: flex;
  visibility: hidden;
  opacity: 0;
}
.dropdown:hover .dropdown-content {
  /*display: flex;*/
  visibility: visible;
  opacity: 1;
  transition: all 0.3s linear;
}