我们可以使用 border 属性设置按钮边框颜色 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    .button {
      background-color: #4CAF50;
      /* Green */
      border: none;
      color: white;
      padding: 15px 32px;
      text-align: center;
      text-decoration: none;
      display: inline-block;
      font-size: 16px;
      margin: 4px 2px;
      cursor: pointer;
    }

    .button1 {
      background-color: white;
      color: black;
      border: 2px solid #4CAF50;
    }

    .button2 {
      background-color: white;
      color: black;
      border: 2px solid #008CBA;
    }

    .button3 {
      background-color: white;
      color: black;
      border: 2px solid #f44336;
    }

    .button4 {
      background-color: white;
      color: black;
      border: 2px solid #e7e7e7;
    }

    .button5 {
      background-color: white;
      color: black;
      border: 2px solid #555555;
    }
  </style>
</head>
<body>

  <h2>按钮边框颜色</h2>
  <p>我们可以使用 border 属性设置按钮边框颜色:</p>

  <button class="button button1">Green</button>
  <button class="button button2">Blue</button>
  <button class="button button3">Red</button>
  <button class="button button4">Gray</button>
  <button class="button button5">Black</button>

</body>
</html>
        