SOURCE

<div class="chat-msg">
  hi, 亲
</div>

.chat-msg {
  position: relative;
  width: 300px;
  height: 80px;
  border: 1px solid #ccc;
  border-radius: 10px;
  padding: 10px;
  margin: 50px auto;
  background: #fff;
  filter:drop-shadow(0 0 2px #999);
  /* box-shadow: 0 0 2px #999; */
}

.chat-msg:before {
  content: '';
  position: absolute;
  left: -10px;
  top: 44px;
  border-top: 6px solid transparent;
  border-bottom: 6px solid transparent;
  border-right: 10px solid #ccc;
}

.chat-msg:after {
  content: '';
  position: absolute;
  left: -8px;
  top: 44px;
  border-top: 6px solid transparent;
  border-bottom: 6px solid transparent;
  border-right: 10px solid #fff;
}