建议：不要使用浮动。它们是一种过时而麻烦的技术，很少有合法的现代用途。
相反，请使用文本对齐、自动侧边距或弹性框。
参见https://css-tricks.com/snippets/css/a-guide-to-flexbox。

body {
  font-family: Arial, Helvetica, sans-serif;
}

.navbar {
  overflow: hidden;
  background-color: #333;
  display: flex; /* <---------------------------------- HERE */
  justify-content: center; /* <------------------------ HERE */
}

.navbar a {
  font-size: 16px;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

.dropdown {
  overflow: hidden;
}

.dropdown .dropbtn {
  font-size: 16px;
  border: none;
  outline: none;
  color: white;
  padding: 14px 16px;
  background-color: inherit;
  font-family: inherit;
  margin: 0;
}

.navbar a:hover,
.dropdown:hover .dropbtn {
  background-color: red;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1;
}

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

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

.dropdown:hover .dropdown-content {
  display: block;
}

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.2.1/css/all.min.css" integrity="sha512-MV7K8+y+gLIBoVD59lQIYicR65iaqukzvf/nwasF0nqhPay5w/9lJmVM2hMDcnK1OnMGCdVK+iQrJ7lzPJQd1w==" crossorigin="anonymous" referrerpolicy="no-referrer" />

<div class="navbar">
  <div class="dropdown" id="one">
    <button class="dropbtn">A
      <i class="fa fa-caret-down"></i>
    </button>

    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </div>

  <div class="dropdown" id="two">
    <button class="dropbtn">B
      <i class="fa fa-caret-down"></i>
    </button>

    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </div>

  <div class="dropdown" id="three">
    <button class="dropbtn">C
      <i class="fa fa-caret-down"></i>
    </button>

    <div class="dropdown-content">
      <a href="#">Link 1</a>
      <a href="#">Link 2</a>
      <a href="#">Link 3</a>
    </div>
  </div>
</div>

创建一个名为center的div并将其设置为内联块

.center{
  display: inline-block;
}

然后用它覆盖你所有的下拉唐斯，就像这里的波纹管

<div class="center">
    <div class="dropdown" id="one">
      <button class="dropbtn">
        A
        <i class="fa fa-caret-down"></i>
      </button>
      <div class="dropdown-content">
        <a href="#">Link 1</a>
        <a href="#">Link 2</a>
        <a href="#">Link 3</a>
      </div>
    </div>
    <div class="dropdown" id="two">
      <button class="dropbtn">
        B
        <i class="fa fa-caret-down"></i>
      </button>
      <div class="dropdown-content">
        <a href="#">Link 1</a>
        <a href="#">Link 2</a>
        <a href="#">Link 3</a>
      </div>
    </div>
    <div class="dropdown" id="three">
      <button class="dropbtn">
        C
        <i class="fa fa-caret-down"></i>
      </button>
      <div class="dropdown-content">
        <a href="#">Link 1</a>
        <a href="#">Link 2</a>
        <a href="#">Link 3</a>
      </div>
    </div>
  </div>

然后添加到你的css文本对齐中心到.navbar

.navbar {
    overflow: hidden;
    background-color: #333;
    text-align:center

  }

现在它将居中这div类.center并且你的下拉菜单项将总是居中
还有其他的方法来做，但是如果你不声明你的div的宽度，这看起来是最好的
下面是正确的完整代码片段
一个三个三个一个