<body>

  <div class="talk">
    สวัสดีชาวโลก
  </div>
  
</body>
body{
  color: #333;
  background-color: black;
}
.talk{
  position: relative;
  padding: 30px;
  width: 200px;
  font-size: 21px;
  text-align: center;
  background-color: #fff;
  border-radius: 5px;
}
.talk::before{
  content: '';
  position: absolute;
  bottom: -20px;
  left: 40px;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 20px 15px 0 15px;
  border-color: #fff transparent transparent transparent;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.