How can I create the above effect in css border?

CodePudding user response：

You can use box shadow for additional border effect. For more detailed examples please check Double border with different color

  <hr> 
  <style>
    body {
      background: #1f1f1f;
    }

    hr {
      border: none;
      height: 2px;
      background: #000;
      box-shadow: 0 1px 0 0 #404040;
    }
  </style>