howto 在线编辑器 | howto代码测试

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>.dropbtn {
  background-color: #4CAF50;
  color: white;
  padding: 16px;
  font-size: 16px;
  border: none;
  cursor: pointer;
}

.dropbtn:hover, .dropbtn:focus {
  background-color: #3e8e41;
}

.dropdown {
  float: right;
  position: relative;
  display: inline-block;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f1f1f1;
  min-width: 160px;
  overflow: auto;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  right: 0;
  z-index: 1;
}

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

.dropdown a:hover {background-color: #ddd;}

.show {display: block;}
</style>
</head>
<body>

<h2>对齐的下拉内容</h2>
<p>在下拉类上使用 <strong>float: right</strong> 使下拉菜单向右浮动，如果您希望下拉内容从右侧移动，则在下拉内容上使用 <strong>right:0</strong> 向左。</p>

<div class="dropdown">
  <button onclick="myFunction()" class="dropbtn">下拉菜单</button>
  <div id="myDropdown" class="dropdown-content">
    <a href="#home">首页</a>
    <a href="#about">About</a>
    <a href="#contact">联系方式</a>
  </div>
</div>

// 如果用户在下拉框外单击，则关闭下拉框
window.onclick = function(event) {
  if (!event.target.matches('.dropbtn')) {
    var dropdowns = document.getElementsByClassName("dropdown-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}
</script>

</body>
</html>

报个问题: