JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">

  <div class="say">
    <p>三角の部分も透過させたいです。<br>そんな吹き出し、できませんか？</p>
  </div>

</div>

CSS

.wrapper {
  padding: 100px 20px;
  background-image: url(http://urx.space/9W4K);
}
.say {
  position: relative;
  display: inline-block;
  margin: 1.5em 0 1.5em 15px;
  padding: 7px 10px;
  min-width: 120px;
  max-width: 100%;
  color: #555;
  font-size: 16px;
  background: transparent;
  border: solid 3px #fff;
  box-sizing: border-box;
}
.say:before {
  content: "";
  position: absolute;
  top: 50%;
  left: -24px;
  margin-top: -12px;
  border: 12px solid transparent;
  border-right: 12px solid #FFF;
  z-index: 2;
}
.say:after {
  content: "";
  position: absolute;
  top: 50%;
  left: -30px;
  margin-top: -14px;
  border: 14px solid transparent;
  border-right: 14px solid #fff;
  z-index: 1;
}
.say p {
  color: #fff;
  margin: 0;
  padding: 0;
}