css/linear-gradient/01tri.html

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>用linear-gradient来实现三角</title>
  <style>
    .talk {
      display: inline-block;
      max-width: 80%;
      border: 1px solid #ddd;
      border-radius: 3px;
      padding: 6px 10px;
      font-size: 14px;
      background-color: #fff;
      position: relative;
      margin-left: 20px;
    }

    .talk::before {
      content: '';
      position: absolute;
      width: 6px;
      height: 6px;
      background: linear-gradient(to top, #ddd, #ddd) no-repeat, linear-gradient(to right, #ddd, #ddd) no-repeat, linear-gradient(135deg, #fff, #fff 6px, hsla(0, 0%, 100%, 0) 6px) no-repeat;
      background-size: 6px 1px, 1px 6px, 6px 6px;
      transform: rotate(-45deg);
      left: -4px;
      top: 13px;
    }
  </style>
</head>

<body>
  <div class="talk">这是对话内容</div>
</body>

</html>